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ATLAS 



OF 



HISTOLOGY 



BY 

E. KLEIN, M.D., F.R.S. 

LECTURER ON HISTOLOGY AT ST BARTHOLOMEWS HOSPITAL MEDICAL SCHOOL 

and 

E. NOBLE SMITH, L.R.C.P., M.R.C.S. 

FORMERLY SENIOR HOUSE-SURGEON TO ST MARY'S HOSPITAL 



WITH FORTY-EIGHT COLOURED PLATES 



THE ILLUSTRATIONS by MR NOBLE SMITH from PREPARATIONS BV DR KLEIN 

THE TEXT by DR KLEIN 



PHILADELPHIA 
J. B. LIPPINCOTT & CO 

LONDON : SMITH, ELDER, & CO. 
l88o 

[Ail rights reserved] 



fart 



Digitized by the Internet Archive 

in 2012 with funding from 

LYRASIS Members and Sloan Foundation 



http://archive.org/details/atlasofhistologyOOklei 



PREFACE. 



->:*« 



This work is intended to be a pictorial and literal representation of the 
structure of the tissues of Man and other Vertebrates ; its chief aim being 
to teach, not so much the history of histology as histology itself in its 
modern aspect. The subject is divided into chapters, each receiving its 
separate and due share of illustrations and text. 

The Illustrations are drawn and executed by Mr. E. Noulk Smith. 
They are coloured and uncoloured. The first represent specimens stained 
with different dyes, to be specially mentioned in the explanation of the 
respective figures. Except, when a figure is rendered in an uniform 
purplish tint, it will be understood to represent a specimen stained with 
hematoxylin ; and likewise, when a figure appears of an uniform pink 
colour, the corresponding specimen is stained with carmine. The 
uncoloured figures are taken either from fresh or unstained specimens, or — 
as is the case in a very few instances specially indicated in the respective 
places — are borrowed from other authors. 

The Text comprises, besides the explanation of the illustrations them- 
selves, a good deal of other matter that either need not be specially 
illustrated, being intelligible by means of the given figures, or that cannot 
be done so if the work is to be kept within a reasonable limit. 

The subject-matter will be treated in this order : first, the elementary 
tissues — blood, epithelium, and endothelium, connective-tissues, muscular 



PREFACE. 

IV 

tissue, the nervous, vascular, and lymphatic system ; then follows a short 
chapter on ' Cells in general,' after which the compound tissues will be 
considered seriatim ; the alimentary canal and its glands, the respiratory 
organs, the urinary and genital organs, the skin and special sense 
organs. The concluding chapter treats of organs the nature of which is 
not sufficiently well known, as the suprarenal capsule, the thyroid and 
coccygeal gland. 



E. KLEIN 



CONTENTS. 



>5*fr 



CHAPTER 

I. Blood 

i. Colourless Blood Corpuscles 
2. Coloured Blood Corpuscles 
Blood Crystals 

II. Epithelium 
III. Endothelium .... 
IV. Connective-tissue Corpuscles 

V. Fibrous-connective Tissue . 

Elastic Tissue . 
Gelatinous Tissue 
Development of Connective 
Tissue .... 

VI. Adipose Tissue 

VII. Pigment Cells . 

VIII. Cartilage 

A. Hyaline Cartilage 

B. Fibrous Cartilage . 

C. Reticular Cartilage 

IX. Bone Tissue . 

Endochondral Bone . 
Intermembranous Bone 

X. Unstriped Muscle 

XI. Striped Muscle Fibres . 

XII. Cerebro-Spinal Nerves 

XIII. The Spinal Cord . 

The Membranes 

A. The Framework 

B. The White Matter 

C. The Grey Matter . 

XIV. The Optic Nerve 



PAGE 
I 

I 

5 
9 

ii 

i9 
26 

35 

36 
38 

39 
42 

45 

48 

48 

50 
5' 

55 
61 
64 

73 

75 
84 

9' 
9' 

93 
94 
95 

99 



CHAPTER 
XV. 



The Brain 

The Membranes 
The Brain Substance 

A. The Framework . 

B. The White Matter 

C. The Grey Matter 
The Cerebellum 



XVI. Cerebro-Spinal Ganglia 



PAi 1 

■ 105 

■ >0 5 
. 106 

. 106 
. 107 
. 108 



1 14 



XVII. The Sympathetic System . .118 

A. The Sympathetic Nerve 

Fibres . . . . 1 1 S 

B. The Sympathetic Ganglia . 119 

XVIII. Peripheral Distribution of 

Nl.RVES . . . .124 

Special Terminal Organs . .127 

A. Pacinian Corpuscles . .127 

B. Endbulbs of the Conjunc- 

tiva . . . . . 129 

C. The Endbulbs of tlie Genital 

Organs . . . .129 

D. The Knd-Organs of the 

Beak and Tongue of Birds 130 

E. Touch-Cells . . . . 130 

F. Termination in Musde . 131 

G. Termination in Tendon . . 133 
//. Termination in Blood- 
vessels . . . .134 

XIX. Blood-Vesskls . . . . 137 

1. Capillary Blood-Vessels . 137 

2. Arteries . . . . 138 

3. Veins *4 2 

4. Development of Blood- 

Vessels .... 145 

5. The Heart . . . . 147 



VI 



CONTENTS. 







PAGE 


CHAPTER 




PACE 


CHATTER 

XX. Lv-MrHATic Glands 


■ 154 




The Uterus 


• 294 




A. Compound Lymphatic 




The Vagina .... 
The Urethra . 


. 298 

. 2QQ 




Glands 
B. Simple Lymphatic Glands 


■ 154 

. 158 




The Nymphse, Clitoris, and Ves 
tibulum .... 


30O 


XXI. 


The Thymus . 

A. The Framework . 


. 165 




The Mammary Gland 


300 




B. The Gland Substance . 


• 165 


XXXIII. 


The Skin .... 
The Epidermis . 


• 307 
307 


XXII. 


Lymphatic Vessels 


. 168 




The Corium 

The Sweat Glands . 


311 
313 


XXIII. 


Teeth, Structure of 


. 181 




The Hair Follicle and Hair 


317 




Development . 


. 184 




The Sebaceous Gland 
The Muscle of the Hair 


322 
X2T. 


XXIV. 


Salivary Glands . 


. 188 




The Nails 


■ 327 


XXV. 








The Blood- Vessels 


329 




I. Mouth and Palate 


194 




The Lymphatic System . 


330 




2. The Tongue . 


197 




The Nerves .... 


332 




3. The Pharynx 


201 










4. The (Esophagus 


201 


XXXIV. 


The Eyelids and Conjunctiva 


335 




5. The Stomach 


203 




The Lachrymal Glands 


340 


XXVI. 


The Small and Large Intestine 


21S 


XXXV. 


The Cornea and Sclerotic 


342 




A. The Small Intestine . . 


215 




The Cornea. 


342 




B. The Large Intestine . 


222 




The Sclerotic . 


348 


XXVII. 


The Pancreas . . . . 


224 


XXXVI. 


The Iris, Ciliary Processes, ane 




XXVIII. 


The Liver 


227 




Chorioidea 


35i 


XXIX. 


The Larynx and Trachea, 






1. The Iris 


35i 




Bronchi and Lung . . 


236 




2. The Ciliary Processes 

3. The Chorioidea . 


353 

354 


■ 


1. The Larynx .... 


236 










2. The Trachea . . . . 


239 


XXXVII. 


The Lens and Vitreous Body 


35 6 




3. The Bronchi 


241 










4. The Lung , . , 


242 


XXXVIII. 


The Retina 


360 


XXX. 


The Urinary Organs 


2 5 T 




i. The Uvea 


360 




The Kidney . . . . 


251 
263 




2. The Rods and Cones . 


361 




The Ureter and Bladder . 




3. The Limitans Externa 


364 








4. The Outer Nuclear Layer 


365 


XXXI. 


The Male Genital Organs . . 


268 




5. The Outer Molecular Layer 


367 




Testis and Epididymis 


268 




6. The Inner Nuclear Layer 


367 




Vas Deferens and Vesicular 






7. The Inner Molecular Layer 


368 


■ 


Seminales 


277 




8. The Layer of Ganglion Cells 


369 




The Prostate Gland 


278 




9. The Layer of Nerve Fibres 


369 




The Urethra .... 


279 




10. The Limitans Interna . 


37° 




Corpora Cavernosa . 


280 




11. The Macula Lutea and Fovea 




XXXII. 


The Female Genital Organs . 


285 




Centralis 
1 2. The Ora Serrata . 


37i 
372 




The Ovary 


285 




13. The Blood- Vessels . . . 


372 
372 
373 




Development of Grafian Follicles 
The Oviduct 


291 
293 




14. The Lymphatics . 

15. The Lamina Cribrosa . . 



CONTENTS. 



VI i 



i I! AFTER 

XXXIX. 



XL. 



The Outer and Middle Ear 

The Membrana Tympani 
The Tuba Eustachii . 
The Cavum Tympani . 



The Internal Ear 

The Utricle, Saccule and 

Semicircular Canals . 
The Cochlea . 
The Membrane of Reissner 
The I.ignmentum Spirale . 
The Membrana Basilaris 
The Organ of Corti . 
The Lamina Reticularis 
The Crista Spiralis . 
The Membrana Tectoria 



the 



PAGI 

3S9 

389 

390 

39' 
393 

393 
39<> 
393 

399 

400 
401 
404 

405 

406 



CHAPTER PAOI 

XLI. The Nasal Mucous Membrane. 409 



The Olfactory Organ 
The Organ of Jacol son 



XL1I. The Spi t EN 



X1.I11. Till Hi 1 11 1 :-s (",| ANDS 



II 1 

433 

43' 



1. The Hypophysis Cerebri . . 431 

2. The Thyroid Gland . . 43a 

3. The Suprarenal Hotly . . 435 

4. The Glandula Coccygea and 

Carotica i.v s 

XL1V. The Indire( i Dn ISION 01 Ni < LEI 439 



LIST OF PLATES, 



•>;« 



PLATE 
I. 


Figures I. -VII. 




Figures VIII. -X. 


II. 


Figures XI.-XYI. 




Figures XVII.-XXI. 


III. 


Figures I. -Villi;. 


IV. 


Figures IX. -XVIII. 


V. 


Figures I. -VII. 


VI. 


Figures VIII.-XIII. 


VII. 


Figures I.-VII. 


VIII. 


Figures VIII.-XV. 


IX. 


Figures XVI.-XXII 


X. 


Figures I. -III. 




Figures IV. -V. 


XL 


Figures I.-VIIL 


XII. 


Figures I. -IV. 


XIII. 


Figures V.-VIII. 


XIV. 


Figures IX.-XIII. 


XV. 


Figures I.-V. 




Figures VL-VIII. 


XVI. 


Figures IX.-XYI. 


XVII. 


Figures L— VI. 


XVIII. 


Figures VII.-XIII. 


XIX. 


Figures I.-VIII. 


XX. 


Figures IX. -XVI I. 




Figure XI. 


XXI. 


Figures I.-VII. 


XXII. 


Figures I.— VI. 




Figure VII. 


XXIII. 


Figures VIII.-XV. 



PAGE 



Colourless Blood Corpuscles 
Coloured Blood Cor] uscles 
Coloured Blood Corpuscles . 
Blood Crystals .... 

Epithelium 

Epithelium 

Endothelium 

Endothelium .... 
Connective-Tissue Corpuscles 
Connective-Tissue Corpuscles . 
Connective Tissue .... 

Fat-Cells 

Pigment Cells . 

Cartilage 

Bone 

Bone 

Bone 

UNSTRIPED Muscle 

Striped Muscle . . . . 

Striped Muscle .... 

Nerve Bundles . 

Nerve Fibres .... 

Spinal Cord 

Spinal Cord .... 

Optic Nerve 

Brain 

Ganglia 

Nerve Ending in Blood-Vessels 
Sympathetic Gancllv and Nerves 



1 v i ription on 



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II II 



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i A 

16 

22 
24 
29 

40 

[6 

52 
67 
69 
71 

Si 

82 

87 
89 



102 



„ 112 



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122 



LIST OF PLA TES. 



PLATE 




xxrv. 


Figures I.-V. 


XXV. 


Figures VI. -XIV 


XXVI. 


Figures I.-IX. 


XXVII. 


Figures X. -XVI I. 


XXVIII. 


Figures I. -VI. 


XXIX 


Figures VII. -XII. 


XXX. 


Figures XIII. -XXII. 


XXXI. 


Figures I.-VII. 




Figures VIII. -IX 


XXXII. 


Figures X-XVII. 


XXXIII. 


Figures XVIII.-XXIX 


XXXIV. 


Figures I.-X. 


XXXV. 


Figures XL-XIII. 




Figures XIV. -XX. 


XXXVI. 


Figures I.-IX. 


XXXVII. 


Figures X.-XIII. 


XXXVIIa. 


Figures I. -III. 




Figure IV. 




Figure V. 


XXXVIII. 


Figures I.-IX. 


XXXIX. 


Figures I.-XIII. 


XL. 


Figures I.-XI. 


XLI. 


Figures I.-IX. 


XLII. 


Figures X.-XVI. 




Figures XVII.-XX. 


XLIII. 


Figures I.-XII. 


XLIV. 


Figures XIII.-XXI. 



Figures XXII.-XXX. 



XLV. Figures I.-XII. 
XLVI. Figures XIII.-XX. 



XLVII. Figures I.-XI. 
XLVIII. Figures I.-VI. 



Figures as. 



Distribution of Fine Nerves . ... 

Nerve Endings 

Blood-Vessels 

Blood-Vessels 

Lymphatic Glands 

Lymphatig Glands 

lvmphatics 

Teeth 

Salivary Glands 

Salivary Glands, Tongue, and Mucous 
Glands 

Tongue, Oesophagus, and Stomach . . . 

Intestines 

Intestines and Pancreas 

Liver 

Respiratory Organs 

Lymphatics of Respiratory Organs 

Kidney 

Spermatozoa 

Ovary 

Kidney 

Male Genital Organs 

Female Genital Organs .... 

Skin 

Skin 

Conjunctiva and Cornea 

Cornea, Sclerotic, Iris, and Chorioidea 

Cornea, Iris, Chorioidea, Lens, and Vitreous 
Body 



Description 


on 


r 34 


11 


H 




135 


» 


>i 




149 


11 


)! 




152 


11 


11 




161 


»i 


11 




163 


ii 


11 




178 



Retina 

The Labyrinth 



The Tuba Eustachii and Nasal Mucous 
Mlmbrane 

The Spleen 

The Ductless Glands 

Indirect Division of Nuclei . . . . 



20S 

210 
212 

231 

233 

247 
249 

264 

265 
2S1 

303 
375 

37S 
33i 

334 

416 

420 
428 

445 



ATLAS OF HISTOLOGY. 



':**:■ 



CHAPTER I. 
BLOOD. 

Blood of vertebrate animals contains suspended in a colourless plasma two kinds of 
corpuscular elements : (a) coloured or so-called red ; and (6) colourless or so-called white 
corpuscles. 

One hundred volumes of blood of man contain about sixty four volumes of plasma 
and thirty-six volumes of corpuscles. 

According to recent measurements (Hayem, Mallassez), there are 4*5 to 5*5 millions 
of coloured blood-corpuscles in one cubic millimetre (or fo cubic inch) of human 
blood. In some animals it is much greater, even as great as eighteen mill, (camels, &c). 
The number varies greatly in different vertebrate animals. In birds it is smaller than 
in mammals, and in fishes it is smallest. The relation between colourless and coloured 
corpuscles in normal human blood varies from 1 for 1,250 to 1 for 650. There is no 
constant increase in the number of colourless corpuscles after meals. The number 
of colourless corpuscles after a meal and simultaneous drinking is increased, but seems 
to be decreased after a meal without drinking. 

The size of coloured corpuscles varies in different vertebrate animals. The largest 
are possessed by amphibian animals (proteus, amphiuma), the smallest by mammals : 
Moschus javanicuSy Meminna and musk deer, have the smallest blood corpuscles. 

[In Rollett's article on Blood in 'Strieker's Handbook' will be found a tabic, by Welker, of 
measurements of blood-corpuscles of the different classes of vertebrate animals. See also Gulliver, 
in 'Proceed. Zoolog. Society of London,' 1874 and 1875.] 

1. Colourless Blood-Corpuscles. 
The colourless blood-corpuscles are spherical, pale, and transparent, when observed 
in the circulating or perfectly fresh blood. In most instances they are larger than the 
coloured corpuscles, but there are in every blood some that are smaller. They possess 

B 



6oi%^ 




2 ATLAS OF HISTOLOGY. 

in no instance a limiting membrane, and are composed of a transparent jelly-like 
substance, called ' protoplasm.' This substance appears more or less distinctly granular ; 
but, on more careful examination, and under suitable conditions (see below), it can be 
shown that it is composed of a very minute network of fibrils (Heitzmann). This network, 
which we shall know as the intracellular network, contains in its nodes minute dots — 
and these produce the granular appearance — which are, however, due to fibrils seen in 
optical section. 

In the meshes of the network is contained a hyaline interstitial substance. The 
accompanying woodcut i shows these relations, and also that the kernel or nucleus 
(in this instance there are two) contains a similar network — 
intranuclear network — which is in direct connection with the intra- 
cellular network. But there are in every blood some colourless 
corpuscles that contain in the meshes of the intracellular network 
coarse bright particles, real granules ; and these corpuscles represent 
granular corpuscles par excellence. In newt's blood, and also in 
human blood, they are often seen in considerable numbers. 
When examined in the fresh state, especially under the influence of heat, e.g. on 
the warm stage, but without the addition of any fluid reagent, the colourless corpuscles 
undergo changes of shape, and in consequence of these also changes of place, just like 
amoebae, and hence the designation of amoeboid movement and amoeboid corpuscles. 
These changes are due to the contractility of the intracellular network. 

In the best examples of human colourless blood-corpuscles examined fresh, without 
any reagent, these changes are sufficiently distinct, even to the unexperienced eye, 
but on applying heat (about blood heat), these movements become very pronounced in 
most of the colourless corpuscles. 

PLATE I. 

Figs. I. II. III. IV. V. VI. and VII. represent colourless corpuscles while 
undergoing changes of shape and place ; drawn under a magnifying power of about 400 
diameters. 

Fig. I. A colourless corpuscle of human blood as observed on the warm stao-e 
in different stages of movement. (The different stages follow each other in this, and the 
following figures, from left to right.) The movement consists in the protrusion of a 
hyaline film. This is withdrawn, and another is protruded ; in the next moment this 
is reduced to a very minute filamentous process, whereas, on the opposite side, a 
new broad process makes its appearance. This alone is left in the next stage. 






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COLOURLESS CORPUSCLES OF BLOOD. 3 

Fig. II. Another colourless corpuscle of human blood while performing amoeboid 
movements. The corpuscle is seen to push out processes of various length and 
thickness, and thus to alter its shape in a considerable manner ; in the last example of 
the lower row the corpuscle has almost separated into two lumps, united by a thin 
bridge. 

Fig. III. A ' granular' corpuscle of newt's blood in three stages of amoeboid move- 
ment while observed on the warm stage. 

Fig. IV. Another granular corpuscle of the same blood in seven different stages of 
movement. The corpuscle showed not only rapid change of shape — there are several 
between each two here delineated — but moved very conspicuously alono- the field of 
the microscope. 

In the 'granular' corpuscles we generally observe that the bright granules are not dis- 
tributed uniformly throughout the protoplasm, but are collected in one or more groups. 
This is entirely due to the presence of large pale transparent nuclei in these corpuscles. 
The pale part in the corpuscles, represented in fig. IV., includes the nuclei but no granules. 
When watching the movements of a ' granular ' corpuscle we often notice a flowing move- 
ment of the granules : this is entirely a passive movement ; the protoplasm itself moves, 
and the granules embedded in it are carried to and fro. 

These 4 granular ' corpuscles are few in numbers as compared with the other pale or 
ordinary colourless corpuscles, and they move much quicker. The greater number of 
colourless corpuscles are pale, indistinctly granular (see above) ; they move generally 
by throwing out finer or thicker, longer or shorter filamentous processes. 

One of the most interesting forms of movement that may be observed in * granular ' as 
well as ordinary colourless corpuscles on the warm stage is this : the protoplasm of the 
corpuscle has collected into two — sometimes even three — lumps, connected by a thin 
bridge of the same substance. Each of these lumps alters its shape and place indepen- 
dently of the other. Now, either of two things may happen : (a) the two lumps move 
away into opposite directions, and by doing so they go on lengthening — at the expense 
of their own substance — the connecting bridge, until this breaks, and each lump, with- 
drawing its part of the bridge, continues to move like an independent individual (Klein) ; 
(6) or the mass of one lump — after a longer or shorter interval — flows again back into the 
other. If the two lumps are of unequal size, the larger one in its change of place is 
capable of dragging the smaller one, except this latter is fixed to the cover glass, or is 
jammed in between groups of blood-corpuscles : in this case the connecting bridge is 
drawn out to great fineness. 

There is another mode of division of a colourless corpuscle into two ; it is by a con- 
striction appearing on the surface of the corpuscle, which after many changes ultimately 

B 2 



ATLAS OF HISTOLOGY. 
4 

cuts through the whole depth of the substance, and thus divides the corpuscle into two 
(Klein, Ranvier). 

In fig. V. a common or pale colourless corpuscle is shown after it has separated into 
two lumps connected by a thin bridge. The lower of the two figures is a later stage of 
movement of the one above. 

In the blood of most vertebrate animals there are other colourless corpuscles besides 
the two kinds mentioned : they are much smaller, possess a relatively large nucleus, and 
show only slight amceboid movement. They represent corpuscles not yet fully developed. 
In newts and frogs blood there are, in addition, oblong pale slightly flattened corpuscles, 
with an oval nucleus : these show only very slight amceboid movement, and are 
supposed to be the intermediary forms between colourless and coloured corpuscles. 

Semmer describes in mammal's blood peculiar nucleated corpuscles somewhat larger 
than ordinary colourless corpuscles, but otherwise similar to them, except that they 
contain red granules, and are therefore called red granular corpuscles ; they are supposed 
by this author and A. Schmidt to be intermediary forms between 'granular' colourless 
corpuscles and coloured ones. 

The plasma of blood of most mammals contains, besides colourless and coloured 
corpuscles, minute bright but colourless, more or less angular granules, isolated or in 
groups (Max Schultze). Their nature is not definitely ascertained ; their number varies 
in different animals and man, and also in one and the same individual at different times. 
If pigment, e.g. vermilion, in a finely divided state is mixed with blood, either 
before or after withdrawing it from the vessels, the colourless corpuscles, in virtue of 
their movement, take up — 'feed on ' — the pigment particles. This process can be easily- 
observed on newt's colourless corpuscles. 

In fig. VI. an ordinary colourless corpuscle is represented that had taken up a few 
vermilion granules ; the other examples represent the same corpuscle while undergoing 
amceboid movement ; the vermilion granules are shifted about in its interior. 

In the same way as a corpuscle takes up pigment granules it is capable also of 
swallowing any other particles of the surrounding medium. In some instances the 
corpuscle is capable of loading itself with a large burden of extraneous matter without 
losing its power of spontaneous movement. But the corpuscle may rid itself again of 
this, by ejecting one particle after another. In fig. VII. a corpuscle is represented before 
and after it has got rid of a portion of its load. 

Many of the colourless corpuscles when fresh and living do not show the nucleus or 
nuclei in their interior ; some, however, show distinct nuclei while moving ; but all 
exhibit their nuclei — from one to four, and even more — when dead, or when treated 
with acids. 



COLOURLESS CORPUSCLES OF BLOOD. 5 

When watching the nuclei of a corpuscle while this is undergoing amoeboid move- 
ment, it may be noticed that the nuclei also change their shape and place within the 
corpuscle ; but this need not be due to any spontaneous movement on the part of the 
nuclei, for it can be readily explained in this way : the nuclei being soft are shifted about 
by the protoplasm within the corpuscle, and are capable of being squeezed into various 
shapes. But the nucleus of the small colourless corpuscles of newt and frog show sponta- 
neous movements (Strieker), owing to the contractility of the intranuclear network. The 
nuclei are generally vesicular in aspect, and, as will be mentioned hereafter, include a minute 
network of fibrils, in some instances also what may be described as a nucleolus. The 
colourless corpuscles swell up on addition of water, and all of them show very distinct 
granules — these being fragments of the disintegrated network — which on a sufficient 
amount of water having acted on the corpuscles exhibit a quick oscillating movement, 
the so-called Brownian molecular movement, shown by any granular matter suspended 
in fluid in a sufficiently finely divided state. The nuclei within the corpuscle swell up 
and become very pale under the influence of water, and finally fuse into one. The 
final effect of water on colourless corpuscles is a total disintegration. 

Under the influence of dilute acid they swell up slightly, the nuclei become distinct 
as irregularly shrunk bodies surrounded by what appears as a granular mass. 

In fig. IX. a colourless corpuscle of newt's blood (the lower corpuscle on the right), 
and in f\g. XVI. of the next Plate one of human blood, is shown under the action of 
dilute acetic acid. 

In alkalies of sufficient strength the colourless corpuscles swell up and become finally 
disintegrated. 

The effect of an electric shock of moderate strength produces a contraction of the 
living colourless corpuscle, after which the corpuscle resumes its movements again. 
Strong currents ultimately cause the corpuscle to swell up and disintegrate just as 
after water (Golubew). 

The colourless corpuscles are regenerated from lymph-corpuscles of lymphatic 
glands and from certain endothelial cells of the serous membranes (see Chapter I II). 

2. Coloured Corpuscles. 

In fishes, amphibias, reptiles, and birds, the coloured corpuscles are elliptical discs of 
an almost uniform yellowish-green tint. A few fishes only (Cyclostomes), and most 
mammals, possess circular discs. Of mammals, only camelus and auchenia have elliptical 
blood-corpuscles. The blood-corpuscles of all mammals are without a nucleus, those of the; 
rest of vertebrate animals have a central nucleus. In no instance have they, when fresh, 
a limiting membrane. They are soft structures and may, by pressure or otherwise, be 



6 ATLAS OF HISTOLOGY, 

brought into various shapes ; they are at the same time elastic and therefore capable of again 
returning to their original form. Under the influence of urea or overheating, the coloured 
blood-corpuscles break up into smaller or larger particles of the same colour and structure 
as when a whole. When extravasated into the living tissues, they also break up into 
smaller or larger particles, which ultimately give origin to amorphous brown pigment. 
The colour of the blood-corpuscles is due to haemoglobin. When isolated they appear of 
a yellowish-green tint, which is of course deeper in a corpuscle seen edgewise than 
flat : only in thick layers do the corpuscles present a red tinge, which increases 
with the quantity of blood-corpuscles. 

In fig. VIII. fresh blood-corpuscles of newt are represented. There are amongst them 
two colourless corpuscles, one of which is an ordinary colourless corpuscle in the act of 
moving — possessed of numerous minute processes ; the other one — to the left and 
above — is a colourless corpuscle of the small kind, undergoing only slight amoeboid 
changes ; below there is a free nucleus of a coloured corpuscle — mechanically pressed 
out. Some of the coloured corpuscles are seen flat, others edgewise, most of them show 
their pale oblong nucleus ; a few of them are slightly shrunk, the haemoglobin 
at the same time being irregularly distributed in them, i.e. some parts of the disc being 
of a lighter, others of a darker tint. 

Under a good power the nucleus of coloured blood-corpuscles of newt, frog, and 
especially toad, show a beautiful delicate network. 

In fig. IX. three coloured and one colourless corpuscle of newt are shown after having 
been acted upon by dilute acetic acid ; the coloured corpuscles have become decolorised, 
presenting now a pale transparent, well-defined disc, and in it the oblong nucleus greatly 
shrunk, and therefore opaque. The colourless corpuscle of this figure has been 
mentioned above. 

In fig. X. coloured corpuscles of newts blood are shown after treatment with a two 

per cent, solution of boracic acid. The result of the action of boracic acid is in this 

instance twofold : a) In some corpuscles the boracic acid produces, 

after a slight swelling, a discolouration of the disc, there being a,t the 

same time an imbibition of the nucleus with colouring matter ; the 

upper three corpuscles are in different stages of this change ; or 

6) the disc is discoloured and the nucleus becomes stained by the 

colouring matter, but is seen to be possessed of minute processes 

2 - which are in connection with fibrils of the disc itself. In some 

instances— not represented here — these latter may be seen to form a network. Thus we 

have to regard the coloured blood-corpuscle as a disc in which a network of fibrils is 

to be distinguished from the transparent ground substance ; this network of fibrils is in 




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COLOURED CORPUSCLES OF BLOOD. 7 

connection with the network forming the nucleus, as represented in the accompanying 
woodcut 2. 

In the blood-corpuscles of newt we have therefore to distinguish : 

a) Network of fibrils of disc. 

b) Interfibrtllar hyaline ground substance of disc: both a and b together form 

the stroma. 

c) Nucleus composed of limiting membrane and network of fibrils in connection 

with those of disc. 

d) Haemoglobin contained in the hyaline ground-substance of the meshes of the 

network of the stroma. 

In some instances boracic acid shows a different effect from the above — viz. a col- 
lection of haemoglobin in the central part of the corpuscle, the haemoglobin not having, 
however, altogether withdrawn from the stroma ; a star-shaped figure of haemoglobin is 
thus produced in the pale disc (Zooid of Briicke). A similar effect may be easily 
obtained in frog's blood after adding water in the proportion of two to one, before 
covering it with a cover-glass (Kneuttinger). 

Water makes the coloured blood-corpuscles — disk and nucleus — to swell up and to 
become entirely deprived of their haemoglobin ; they are then very pale and transparent, 
with very faint outlines. 

PLATE II. 

Figs. XI. -XVI. represent human blood-corpuscles as seen with a magnifying power 
of about 400. Figs, XVIL-XXI. are blood crystals viewed with a lower power — about 
200-250. 

Fig. XI. Human blood in a fresh microscopic specimen made without the addition 
of any fluid. There are two colourless corpuscles in the act of moving, being possessed 
of minute processes. The other corpuscles are coloured ones, most of them arranged 
in rouleaux-form, and thus seen edgewise; the cause of this appearance, always observed 
in similar microscopic specimens of any mammalian blood, is not known. There are 
several isolated corpuscles seen in profile — they appear biconcave ; when seen from the 
broad surface — as shown in two other isolated examples — they appear as circular discs, 
which show a transparent centre and a more opaque peripheral part of a yellowish tint. 

Note. When focussed well, the corpuscle, seen from its broad surface, shows greater transpa- 
rency in the centre than in the periphery, the former being at the same time less tinted than the 
latter. The reason is very simple : the corpuscle being a biconcave disc, is thinner in the centre 
than in the periphery, and therefore less haemoglobin is present in the former than in the latter. 
In many books (Quain, Kolliker, Frey, Rollett, Ranvier) the coloured corpuscles are delineated as 



3 ATLAS OF HISTOLOGY. 

if showing an opaque centre and a light periphery, but they appear such only because it is meant 
to convey that the former is out of focus when the latter is in focus. 

In every preparation of mammals' blood and man there are a few coloured corpuscles conspi- 
cuous amongst the rest by their smallness ; they are called mycrocytcs. They have been found 
very numerous in pernicious anaemia (Osier). Hayem regards them as young growing corpuscles, 
being more numerous in all cases — physiological and pathological — in which a reparation of blood 
occurs, e.g. menstruation, loss of blood, in convalescents after acute diseases, &c. 

Fig. XII. Human blood-corpuscles in | per cent, solution of common salt. The 
coloured blood-corpuscles have become horsechestnut-shaped. When mammalian blood 
is diluted with saline solution or any other indifferent fluid, e.g. solutions of neutral 
salts in a certain percentage, serum or kindred fluids, or if blood be spread out in a very 
thin layer under a cover glass, without the addition of any reagent, the coloured corpuscles 
undergo the following changes : they lose their smooth circular outline, and become 
possessed of minute angular prominences — crinate ; these increase in number, and are 
gradually distributed over the whole surface of the corpuscle, and the corpuscle losing 
its discoid shape, becomes more like a sphere slightly flattened, — horsechestnut-shape : 
the more this last stage is reached the smaller the corpuscle. 

If to corpuscles after having become crinate, like those in fig. XIII. A, carbonic acid 
gas be added, their outline again becomes smooth and circular, but the corpuscles 
generally do not resume their biconcave form, most of them becoming convex- 
concave, i.e. saucer-shaped, like those represented in fig. XIII.b. 

The most probable explanation of the phenomenon of the crinate and horsechestnut- 
shaped corpuscles is this : when blood is removed from the vessels and spread out in a 
thin layer or diluted with an indifferent reagent, a disturbance in the equilibrium of the 
carbonic acid of the plasma and corpuscles must necessarily take place ; in consequence 
of the loss of carbonic acid by the plasma, a loss of carbonic acid is also suffered by the 
corpuscles, and this is followed by the shrinking (coagulation ?) of a part of the stroma — 
probably the network of fibrils; — the more perfect this contraction of the network the 
smaller and the more spherical the corpuscle, and hence also the more horsechestnut- 
shaped. On adding carbonic acid to the corpuscle the network resumes its previous 
character, and the former discoid shape is restored. 

If the coloured corpuscles of mammal's blood are subjected to a succession of electric 
discharges of a Leyden jar, they also lose their smooth outline, becoming first crinate, 
then horsechestnut-shaped, and finally, after having swollen up again, they become 
decolorised (Rollett). 

Figs. XIV. and XV. represent coloured corpuscles of human blood after the addition 
of 2 per cent, tannic acid. The blood-corpuscles (suspended in plasma diluted with 
% per cent, saline solution) were allowed to become crinate and horsechestnut-shaped 



COLOURED CORPUSCLES OF BLOOD, 9 

before the addition of tannic acid. On this latter being added in sufficient quantity, the 
blood-corpuscles are seen to undergo changes represented in fig. XV., i.e. a collection of 
the haemoglobin in one, two or more droplet-shaped masses— they are occasionally 
fanlike — takes place at the periphery of a pale disc, which in some instances is single, 
in others double. In other cases each blood-corpuscle presents at the periphery of a 
decolorised disc a highly refractive, smaller or larger, particle (Roberts), which may be 
easily stained by passing dyes through the specimen. The appearances delineated in 
figures XIV. and XV. are no doubt analogous— viz. being due to a separation of the 
haemoglobin from the stroma of the blood-corpuscles. 

Fig. XVI. When to human blood a weak acid, e.g. dilute acetic acid, is added, the 
coloured corpuscles are decolorised and converted into pale circular discs, each with a 
sharp outline ; in the colourless corpuscles the small nuclei are brought out, as 
mentioned above. 

The coloured corpuscles are formed from colourless ones, these altering in shape and 
the hyaline ground-substance, contained in the meshes of the intracellular network, 
becoming filled with haemoglobin. 

In the foetus all blood-corpuscles are at first colourless; these soon become converted 

into coloured ones, which even in mammals retain the nucleus for a short period. 

Bottcher, however, maintains that also the adult coloured corpuscles possess a nucleus. 

It is doutbful whether what Bottcher demonstrates is a nucleus at all. 

According to Neumann and Bizzozero, the marrow of bones of mammals contains 

nucleated coloured blood-corpuscles, i.e. intermediary forms between colourless and 

coloured corpuscles. 

Blood Crystals. 

Fig. XVII. Haemin-crystals of human blood. The amorphous blood-pigment 
(Haematin) obtained by the decomposition of haemoglobin can be converted, by 
means of chlorides, into nut-brown rhombic crystalline plates, hamin or Tcichmann's 
crystals, i.e. hydrochlorate of haematin. They are formed when dry blood is decom- 
posed by glacial acetic acid in the presence of chloride of sodium (common 

salt). 

In most cases the crystals are notched in at the narrow sides, at the same time 

they do not appear quite flat, but slightly trough-shaped. 

Fig. XVIII. Haematoidin-crystals. 

Red-brown crystalline needles, singly or in bundles, found in extravasated blood. 
In the present instance the crystals are contained in blood that had been extravasated 
into the submucous tissue of intestine of pig. 

c 



10 



ATLAS OF HISTOLOGY. 



The so-called bloocl-crystals par excellence are the haemoglobin crystals ; in many 
kinds cf blood they represent rhombic plates of a bright crimson colour, when obtained 
from a sufficient quantity of blood. In most mammals they are rhombic plates, e.g. 
fig. XXI. (copied from Preyer's book on ' Blood-crystals') ; in the guinea-pig they are 
tetrahedral (fig. XX.), and in the squirrel hexagonal plates. 

Haemoglobin crystals of ox and pig are very difficult to obtain, or not at all. 
Figure XIX. represents haemoglobin crystals (?) of blood of pig; they were seen 
in a very thin layer of fresh blood two to three days after having been mounted as 
a microscopic specimen. The animal from which the blood had been obtained was 
diseased, 



1 1 



CHAPTER II. 
EPITHELIUM. 

Epithelial cells are nucleated cells covering mucous membranes and skin, or lining 
secreting or kindred glands. The epithelial cells vary in shape and arrangement. They 
are columnar or pavement cells : the former again — conical, cylindrical or prismatical, 
spindle-shaped, pear-shaped or club-shaped ; the latter — tessular or cubical, polyhedral 
and more or less flattened, scaly or squamous. 

In this chapter will be considered the epithelium covering the skin and mucous membranes 
only; the epithelium of glands will be treated in connection with the latter in later chapters. 

As regards their arrangement, epithelial cells form either simple columnar or simple 
pavement epithelium, i.e. are arranged in a single layer, or they aggregate into stratified 
columnar or stratified pavement epithelium, formed of several layers of columnar cells 
(of various shapes), or of several layers of pavement cells (of various shapes). As 
regards the substance of the epithelial cells, it is invariably composed of what appears 
at first sight as 'granular' protoplasm, but what is in reality (when examined under 
certain favourable conditions) a minute network (Heitzmann, Eimer, Klein) — intra- 
cellular network. The meshes of this network contain a hyaline interfibrillar substance, 
the amount of which determines the closeness of that network. The intracellular 
network is uniformly distributed throughout polyhedral cells — like that represented in 
woodcut 3 — but it possesses a longitudinal arrangement in columnar 
cells like the one represented in woodcut 4 ; i.e. the greater number 
of fibrils run parallel with the long axis. In all instances, how- 
ever, there are small dots or 'granules ' seen in the network, chiefly 
in the nodes, which are fibrils viewed in optical section, hence the 3* 

1 granular ' appearance is the more, distinct the closer the network, i.e. the more 
numerous the fibrils. 

Some epithelial cells possess a fine limiting membrane, others are without it ; thus, 
for instance, most columnar epithelial cells have a membrane, so also the squamous 
epithelial cells of the superficial layers of stratified epithelium, whereas the polyhedral 
cells of the deeper strata of the latter are without it. But wherever it is present, it is 
merely a denser part of the cell-substance, probably in consequence of a process of 
( hardening,' due to evaporation. 

c 2 




l2 ATLAS OF HISTOLOGY. 

The nucleus of epithelial cells is oval in most columnar cells, spherical or nearly so 
in polyhedral cells ; the more flattened these latter the more flattened also their nucleus. 
The nucleus consists of a limiting membrane and contents ; this latter is a minute 
network (Fromann, Flemming, Eimer, Klein) — intranuclear network ; and in the 
meshes of it a hyaline substance. The small dots or * granules ' present in the meshes 
of this network are due, like those of the intracellular network, to fibrils viewed in 
optical section. Besides these there are contained in the intranuclear network occa- 
sionally — but not very frequently — one or more larger highly refractive particles 
(nucleoli), which in some instances represent the remnants of the primary substance 
out of which the intranuclear network has developed ; in other instances they are 
part of the shrunken network. Epithelial cells are grouped together by the aid 
of a homogeneous clear semifluid albuminous substance, which is placed in thin layers 
between the individual cells ; hence it is termed ' intercellular cement,' or simply 
'cement substance.' In sections through hardened specimens this cement-substance 
presents itself as a fine membrane separating neighbouring cells, but in the fresh state 
it is clear and viscid. Into this substance extend, from the subepithelial membrane, 
branched cells and their processes — connective-tissue cells (see further below). We 
shall have to return to this cement-substance on a later occasion. 

Owing to the soft condition of the cell-substance and the semi-fluid nature of the cement- 
substance, the epithelium covering a membrane is capable — temporarily of course — of changing to 
a certain extent its character, if this latter (membrane) is subjected — in a natural or artificial 
manner — to certain mechanical alterations, such as contraction and expansion. If e.g. the mem- 
brane be greatly expanded, the epithelium, if stratified, becomes less stratified ; or if only in a single 
layer, its cells become shorter in a vertical diameter, i.e. become flattened. If on the contrary the 
membrane shrinks ad maximum, the epithelium, if stratified, becomes more so, and if in a single 
layer, its cells become longer in a vertical diameter, i.e. thicker. 

Both columnar as well as pavement epithelial cells are occasionally provided on 
their free surface with a smaller or larger bundle of fine hairs— cilia, which are prolonga- 
tions of the fibrils of the intracellular network, as represented in 
woodcut 4, projecting through the thin membrane covering the free 
cell border. These cilia during the living condition of the cell are 
all simultaneously in rapid to-and-fro motion. It is quite possible 
that this movement is caused by the contraction of the intracellular 
network in this way : supposing the intracellular network contracts 
to one side in a horizontal diameter, each such contraction acts 
naturally on the lower end of the cilia, which thereby are pulled to 
the same side, while the outer or freely projecting portion of the 
cilia is driven in the opposite direction, each cilium representing a lever, the short arm 




CILIATED EPITHELIAL CELLS. 13 

of which is within the cell in connection with the intracellular network, the long; arm 
being the freely projecting part, and the fulcrum or fixed point lying in the membrane 
covering the free cell-border. When in the next moment the contraction of the intra- 
cellular network ceases the cilia move again in the opposite direction. These two 
phases would correspond to the to-and-fro movement of the cilia. 

When ciliated cells are stimulated with moderate electric currents, the movement, 
if it has become slow, is again accelerated (Engelmann). Slight heat increases likewise 
the movement. And the same effect is produced to a certain extent by any fluid-current, 
no matter what it contains (Klein) ; not merely by liquor potassii, as often assumed, 
but by any other fluid ; it is probably the mechanical stimulation produced by the 
current that acts on the ciliary movement. Carbonic acid added in sufficient quantities 
slackens and then arrests the movement ; replacing it by air, the movement sets in again. 
But in the first place the addition of carbonic acid, just like the addition of any other 
reagent, produces an acceleration of the movement. All those reagents which, when 
added in sufficient quantities, destroy or impair the movement of amoeboid cells have 
the same effect also on ciliary movement. 

Columnar epithelial cells that reach a free surface, no matter whether they are 
ciliated or not, undergo occasionally a change of shape, which is associated with 
the secretion of mucous by them (F. E. Schulze) ; it consists in the conversion of the 
hyaline interfibrillar or interstitial substance, i.e. the hyaline substance contained in the 
meshes of the intracellular network, into hygroscopic mucin, and consequently the 
swelling up of it. Owing to the bulk of the cell-substance occupying the part of the 
cell nearest the free surface (see woodcut 5), and owing to the cell being covered on 
its free surface with a membrane, the swelling up of the interfibrillar substance pro- 
duces a change of shape of the cell — from a columnar cell into a goblet- 
shaped element — goblet cell (see woodcut 6). It is intelligible how 
the nucleus, with a small portion of protoplasm surrounding it, is pressed 
into the distal end of the cell (see woodcut 6). The membrane 
covering the free border of the cell ultimately becomes detached, and, 
in the case of the ciliated cell, of course also the cilia fixed in it — and 
the mucus is finally poured out The mucous contents of these goblet 
cells stain deep purple-blue in hematoxylin, and thus obscure the intracellular net- 
work, whose meshes are now much larger. 




I4 ATLAS OF HISTOLOGY. 



PLATE III. 



Figs. I. II. IV. V. VI. VII. VI 1 1. a are drawn under a magnifying power of 
about 350. Figs. III. and VIII. b under a magnifying power of about 550. 

Figure I. Epithelial cells of trachea of dog, in groups and isolated. Those that 
reach the free surface of the membrane are provided with fine cilia ; they are conical* 
their free basis directed towards the surface. Between these fit others, more or less 
spindle-shaped or of an inverted conical shape, having their pointed extremity directed 
upwards — stratified columnar epithelium. Both the basis of the latter and the pointed 
extremity of the former and latter are provided in many instances with two or more 
fine branches. An oval nucleus is found in each superficial cell. 

Some of the minute details of structure are not shown in this or many of the following drawings 
of Plates III. and IV., since the shape and arrangement of the cells is at present our principal 
object. 

Fig. II. From a transverse section through the trachea of cat, showing the stratified 
epithelium composed of the superficial conical cells with cilia and the deeper non- 
ciliated cells of an inverted conical shape, i.e. their base directed downwards. This 
base contains the spherical nucleus. In the right section of the figure some of the 
superficial cells have lost their cover and cilia, and are goblet cells containing mucus 
which is being poured out. Underneath the epithelium is seen a connective-tissue 
membrane with the nuclei of the connective-tissue corpuscles ; these latter are not 
represented ; and finally underneath this layer is one that contains a great number of 
bright dots, being the cut ends of elastic fibres running a longitudinal course. 

A similar stratified columnar epithelium (ciliated) is present in other parts of the re- 
spiratory tract ; e.g. nasal cavity, larynx (except the epiglottis, the true and part of the false 
vocal cords) and larger bronchi. The central canal of the spinal cord, the small bronchi, 
the fundus uteri and the oviduct contain simple columnar epithelium with cilia. So does 
also the mucous membrane of the mouth, pharynx and oesophagus of amphibian 
animals. 

Fig. III. The first (unlettered) cell is a goblet cell of stomach of newt, showing the 
intranuclear network in connection with fibrils of the intracellular network ; the upper 
part of the cell is greatly swollen up by the presence of mucus, stained slightly with 
carmine. 

a) A nucleus of a glandular epithelial cell of stomach of newt, showing the intra 

nuclear network. 

b) A similar nucleus of an epithelial cell of the surface of the same organ. 



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GOBLET CELLS OF INTESTINE. 15 

c) An epithelial cell of the surface of the same organ, showing the intracellular 

fibrils ; the network of these is not well seen. 

d) An isolated fragment of the intranuclear network of an epithelial cell of the 

same organ. 

Fig. IV. Columnar epithelial cells lining the surface of the mucous membrane of 
large intestine — simple columnar epithelium. Some of the epithelial cells are goblet 
cells pouring out their mucous contents. 

The same relation exists in the simple gland tubes situated in the mucous membrane 
of the small and large intestine — crypts of Lieberkuhn. The epithelium lining them is 
a simple columnar epithelium, and some of its cells are in a state of mucous secretion, 
i.e. are goblet cells. The number of these varies in different animals, in different states 
of digestion, and under different reagents. Thus they are most numerous in carnivorous 
animals during digestion, and in preparations treated with a chromium compound, e.g. 
chromic acid, bichromate of potash, M tillers fluid, chromate of ammonia. This refers 
both to the epithelium covering the free surface of the mucous membrane of the 
intestine, and to those lining the crypts of Lieberkuhn. 

Figs. V. and VI. represent such crypts transversely cut; fig. VII. the same cut 
longitudinally — at any rate, the greater part of the tube is cut longitudinally. 

Figs. V. and VII. are from the large intestine of pig ; fig. VI. from that of cat. In 
this last-named figure the capillary blood-vessels— cut in different directions — sur- 
rounding the crypts are injected with carmine gelatin. 

Fig. VIII. A vertical section through the epithelium covering the skin — epidermis. 

The epidermis is composed of the following different strata : 

a) Rete Malpighii or rete mucosum. 

b) Granular layer (Langerhans). 

c) Stratum lucidum (Schron). 

d) Stratum corneum. 

a) The rete Malpighii is a stratified pavement epithelium, composed of a deepest 
layer of more or less columnar cells each with an oval nucleus ; then follow several layers 
of polyhedral cells, each with a more or less spherical nucleus. Towards the surface the 
cells and their nuclei become more flattened. The lower surface of the rete Malpighii 
is not flat, but adapts itself to the minute papilla with which the surface of the true 

skin is provided. 

6) The granular layer, or more appropriately called the layer of the granular cells, is 
a stratum of flattened cells, spindle-shaped looking in vertical section, each with a 
more or less distinct clear nucleus, from the poles of which extend rod-like or disc- 



l6 ATLAS OF HISTOLOGY. 

shaped granules, gradually diminishing in size from the nucleus outwards. These 
granules stain deeply blue in hematoxylin, and thus become very conspicuous. 

c) The stratum lucidum is a bright homogeneous or indistinctly striated membrane, 
composed of closely packed scales, in some of which minute traces of a staff-shaped 
nucleus may be occasionally distinguished. As a rule it is homogeneous. 

d) The stratum corneum is composed of many layers of horny cuticles, each of which 
is composed of horny non-nucleated scales. They are best shown in liquor potassii. 

The thickness and distinctness of these various layers is very different in the skin 
of different regions. 

The rete Malpighii is the one stratum that alters least in its thickness, whereas the 
stratum corneum of some parts, e.g. of the volar side of the hand and plantar side of the 
foot, many times surpasses in thickness that of other parts. Also the stratum lucidum 
and the granular layer are in some places more distinct than in others ; they are generally 
best developed at and near the mouth of hair follicles, and also near the nails. 

The cells of the deepest layer of the rete Malpighii contain, in coloured skins, a 
considerable amount of dark pigment granules ; these are generally accumulated in the 
cell-substance around the nucleus. 

The polyhedral cells of the rete Malpighii are connected with each other by fine 
filaments (Bizzozero, Heitzmann), the so-called prickles of the prickle-cells (Max 
Schultze). In fig. VIII. b this is well shown. The substance of these cells is not simply 
granular, but it is a very dense network, and the prickles are fibrils uniting the net- 
work of adjacent cells ; but the cells are separated from each other by the ordinary 
transparent cement-substance mentioned above. Under inflammatory conditions this 
intercellular substance increases to a considerable extent, and hence the cells become 
more separated from each other, and the prickles or connecting filaments, on account of 
their greater length, are then better seen. 

The same condition, i.e. prickle cells, is noticed also in stratified pavement epithelium 
other than the rete Malpighii, e.g. the stratified pavement epithelium covering the 
mucous membrane of the mouth. 



PLATE IV. 

Fig. IX., drawn under a magnifying power of about 550; the other figures under a 
magnifying power of about 350. 

Figs. IX. and X. Simple columnar epithelium covering a villus of small intestine, 
goblet cells amongst them. Besides the oblong nuclei belonging to the columnar 
epithelial cells there are several round nuclei of lymph-corpuscles ; these are not, how- 
















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COLUMNAR EPITHELIAL CELLS. i 7 

ever, contained in the substance of the epithelial cells themselves, but between these 
latter— i.e. below or above those represented in the figure. The columnar epithelial 
cells show on their free border a fine striation. These striae, as shown in woodcut 5, are 
prolongations of the fibrils of the cell-substance. Usually these striae are represented as 
if contained in a broad bright cuticular substance covering the free surface of this 
epithelium; but, as is seen in figs. IX. and X., these striae or fibrils may be 
present without such bright cuticle, so that this latter cannot be actually covering the 
epithelial cells, but is probably due to a prolongation of the intercellular cement- 
substance, and thus in a profile view it appears as if covering the free surface of the cell 
itself, although in reality it is above or below it. 

Fig. XI. Fresh epithelial cells of mouth of frog. Three are ciliated, one is without 
cilia ; the two cells to the left appear as if spheroidal in shape, but in reality they are 
columnar, just like the third ciliated cell in this figure, only the former are viewed 
obliquely. 

Fig. XIII. Scaly epithelial cells contained in saliva of mouth of man. They are 
derived from the superficial layers of the stratified epithelium of the mucous membrane 
of the mouth. Four cells are seen from the broad, one from the narrow surface ; one 
spherical granular cell, a so-called salivary corpuscle with a nucleus in it. These salivary 
corpuscles, probably derived from amceboid corpuscles that have emigrated from the 
mucous membrane, appear somewhat swollen up, owing to the influence of the watery 
saliva ; their granules are in a rapid oscillation (Briicke), just as in the colourless blood- 
corpuscles treated with water. 

Figure XIV. Vertical section through the epithelium covering the anterior surface 
of the cornea. The epithelium is stratified pavement epithelium, of a similar arrange- 
ment as the rete Malpighii of the epidermis, or as the epithelium lining the mucous 
membrane of the mouth, of the lower part of pharynx and of the oesophagus of mammals, 
the vagina, the fossa navicularis of the male urethra, part of the male and female urethra. 
The epithelium of these different organs varies in the number of layers and in the 
presence of larger or smaller papillae of the mucous membrane. According to the 
length of these the epithelium projects against the mucous membrane as longer or 
shorter interpapillary processes. The membrane of the cornea not possessing any 
papillae is therefore covered by an epithelium with smooth under-surface. 

The very different shapes presented by the columnar cells of the deepest layer of 
stratified pavement epithelium suggest that by horizontal division they produce the 
polyhedral cells above them, a proposition that can be proved by careful examination 
of isolated cells. The cells of the lowest stratum elongate, and by so doing have to 
adapt themselves to the space available to them. Thus some are club-shaped, pear- 

D 



lS ATLAS OF HISTOLOGY. 

shaped, or columnar ; their nucleus divides into two, and then also the cell divides 
horizontally, and thus gives origin to a polyhedral cell above and a short columnar 
cell below (Lott, Rollett). This last one again elongates, &c. The cells of the 
deepest layer are in different stages of this process. As the production of the poly- 
hedral cells by the deepest cell-layer proceeds, those first formed are pushed towards the 
surface by those formed last, and the nearer they are brought to the surface the more 
flattened do they become (as well as their nucleus). Those on the surface are sub- 
jected to evaporation and hornification, and in consequence of mechanical influences 
they become gradually removed altogether. 

Between the cells of the stratified pavement epithelium are seen from place to place 
branched nucleated cells — connective tissue cells ; in fig. XII. we see these in a surface- 
view of the deeper layer of the epithelium of the cornea. The processes of these cells 
become identified with the intercellular cement-substance ; this is well shown in figure 
XV., representing the epithelium covering one side of the tail of a tadpole, viewed from 
the surface. These branched cells are seen to extend with their processes amongst the 
epithelial cells; the two upper ones are pigmented, the third lower one is quite colourless. 
Fig. XVI. is a vertical section through the stratified pavement epithelium covering 
the (true) vocal cord of man ; the epithelium is placed on a thick homogeneous elastic 
basement membrane. Some of the most superficial cells have become altogether 
detached. 

The epithelium lining the alveoli of the lung is a simple pavement epithelium (see 
the chapter on Lung). 

The epithelium lining the mucous membrane of the urinary bladder is stratified 
epithelium, of which the most superficial layer is composed of polyhedral cells of various 
sizes, each with one, two, or three nuclei— Figure XVII., and several other layers of 
columnar cells, which are club-shaped and spindle-shaped ; those next the superficial 
layer of polyhedral cells are large club-shaped cells, those of the depth are smaller and 
more spindle-shaped ; each has an oval nucleus— Fig. XVIII. 

This stratified epithelium is therefore a mixed epithelium, and is generally called 
transitional epithelium. Similar transitional epithelium may be found at those places 
where stratified columnar epithelium passes into stratified pavement epithelium, 
e.g. larynx, upper part of palate, upper part of pharynx, &c. 

The polyhedral (hexagonal) cells covering the external layer of the retina, and 
containing in most animals (except albinos) dark pigment granules, will be specially 
described in the chapter treating of the Retina. 



19 



CHAPTER III. 
ENDOTHELIUM. 

Endothelium is understood to be the layer of flattened cells lining the free surface of 
any membrane, or cavity, or canal that is not a mucous membrane, or that is not the 
cavity or canal of a secreting gland respectively. The cells of these structures are- 
epithelial cells, they form the epithelium, and are derived, as a rule, from the epiblast or 
hypoblast of the embryo. The cavities of the heart, of all blood-vessels and lymphatic 
vessels, lymphatic sacs and sinuses, the free surface of all serous and synovial mem- 
branes, the cavity of the tendinous sheaths, the subdural and subarachnoidal cavities, 
the chambers of the eye, &c, are lined with cells which form the endothelium. 

The endothelium, in common with connective-tissue cells, to which it is closely 
related, and with which it forms a continuous group, as will be shown below, is derived 
from the mesoblast of the embryo. It is composed, with few exceptions, of a single 
layer of flattened cells — endothelial cells — each of which consists of a transparent 
elastic plate with an oval nucleus generally situated excentrically. The cells are held 
together by the same semifluid albuminous cement-substance mentioned at the 
epithelium. On account of the nucleus being thicker in vertical diameter than the cell 
itself, this latter, when viewed in (real or optical) vertical section, appears spindle-shaped. 

A careful examination of the endothelial plates of different regions (blood-vessels, 
serous membranes, lymphatic sacs) in the fresh state, but still better after reagents, 
shows that their substance is not homogeneous, but possesses within a hyaline grotind- 
plate a plexus of minute fibrils, which in many places are again connected with each other 
so as to form a network— intracellular network (Klein). The nucleus of each endothelial 
plate contains— like other nuclei— within a limiting membrane a dense network of fibrils — 
intranuclear network. This latter is connected by minute fibrils with the network of the 
cell itself. In those nuclei which may be regarded as in a ripe state the intranuclear 
network is uniform in its structure, other nuclei— probably in different stages of unripe- 
ness-possess one, two, or more large particles-nucleoli-included in the network. 
But in most cases we find also here the small bright dots-optical sections of fibrils- 
in the nodes of the network. Most endothelial cells possess a single oval nucleus with 
smooth outline, and in a given group most of the nuclei are approximately of the same 
size. But there are always isolated cases where one cell contains either two nuclei, 

E 



, ATLAS OF HISTOLOGY. 

or one conspicuously large nucleus with or without indications of division, being hour- 
glass shaped, kidney-shaped, or lobate. On account of the very slight difference in 
refractive power of the endothelial cells, and the intercellular cement-substance, the 
outlines of the former cannot be easily ascertained. But with the aid of nitrate of 
silver this difficulty is entirely obviated (v. Recklinghausen). Any membrane covered 
with endothelium when steeped in a dilute solution of nitrate of silver (| — \ per cent.) 
for a few minutes, after exposure to the light, shows the outlines of the individual cells 
of the endothelium with great distinctness, the cement-substance being now visible as a 
black line. 

The substance of the cells themselves and their nucleus is, as a rule, under these circumstances 
— except after prolonged staining with nitrate of silver — not discernible. Sometimes the former is 
recognisable by a granular precipitate, the latter being then noticeable as a clear space. But by 
staining with carmine or hematoxylin or other dyes, the nucleus of the endothelial plates can 
be always very prominently brought out. 

A comparison of the endothelium of different organs shows considerable differences 
as regards the shape and outline of its cells. Thus, for instance, the endothelial cells 
lining small arteries and small lymphatic vessels are very elongated (flattened) with 
tolerably smooth outlines, whereas those of veins are less elongated, and their outlines 
are much more crinate and wavy. Again, the endothelial cells lining the large lymph- 
sacs of batrachian animals (subcutaneous and internal lymph-sacs), or those lining the 
so-called lymphatic capillaries, are more or less polygonal with a wavy or sinuous out- 
line. Or, the endothelial cells covering the mesentery, the pleura, and pericardium of 
mammals are polyhedral cells with straight outlines. 

But in every 7 given place there are certain irregularities consisting in some cells 
deviating more or less in shape and outline from their neighbours. 

The endothelial plates being elastic, and their interstitial cement-substance very 
soft, they, just like epithelium mentioned in the preceding chapter, are capable of 
altering their shape, size, and thickness, according to the state of contraction or 
expansion of the subjacent membrane, or the direction in which this is being drawn. 
If, for instance, the omentum, or the mesentery, or any other delicate membrane 
covered with endothelium, be drawn in a certain direction — of course within 
reasonable limits, so as not to disturb the continuity of its elements — the endothelial 
cells will be found to become elongated in the same direction, and if the membrane be 
then brought back to its former state, or drawn into a different direction, the endothelial 
cells will be found to change their shape accordingly. And also their outline may 
undergo corresponding variations ; viz. it may be straight, or wavy, or sinuous, 
according to the state of expansion or contraction of the membrane. 

The endothelial plates vary in size in the different organs, and also in one and the 



GERMINATING ENDOTHELIUM. 21 

same organ in different parts. Thus, for instance, they are considerably larger in the 
subcutaneous lymph-sacs than in blood-vessels of frog ; in mammals they are far larger 
in the sheaths of tendons and nerve-bundles than in serous membranes, and amongst 
these the omentum is covered with larger endothelial plates than the pericardium. In 
many instances we find, however, isolated, or larger or smaller, groups of endothelial 
plates smaller than their neighbours, they are at the same time less flattened, more 
polyhedral, and even in the fresh state easier recognised, on account of their substance 
being more ' granular,' less transparent than that of the ordinary large flat endothelial 
plates. The nucleus of these small polyhedral cells is either single, or in a state of 
division, or it is already divided into two. These cells represent germinating endothelial 
cells (Klein). They are present in many serous membranes of young and adult indi- 
viduals, on synovial membranes, on the tunica albuginea testis, on the endocardium of 
young individuals. They acquire a very great extension under pathological processes. 

The omentum and pleura mediastini of mammalian animals are especially rich in 
smaller or larger groups of such germinating endothelial cells. In many instances they 
are found on the surface of special thickenings of the normal membrane — to be described 
in a later chapter — which present themselves to the unaided eye, according to their size, 
as larger or smaller opaque patches, nodules, or cords, many of them in connection 
with the vascular system. In some instances the germinating endothelial cells are 
found on peculiar villous or papillary projections, found especially under pathological 
conditions, — e.g. chronic, and also acute inflammations — in serous and synovial mem- 
branes, in the processus vaginalis and tunica albuginea testis, and the membranes of the 
central nervous system. 

In some cases, e.g. omentum and pleura mediastini, the germinating endo- 
thelium contains cells which are in the act of division, or such as are becoming 
gradually altogether detached from the membrane. In the latter instance we find them 
club-shaped or pear-shaped, and connected with the membrane by a thinner or thicken 
longer or shorter stalk. When this breaks the cell is free of the membrane. While in 
the process of detaching itself the cell becomes possessed of the power of amoeboid 
movement, and it thus also in this important character approaches the nature of a 
lymph-corpuscle or colourless blood-corpuscle. After these cells have become freed of 
the membrane, they find their way into the lymphatic vessels, and hence into the blood- 
vessels, as colourless blood-corpuscles. In many mammals the amount of such germi- 
nating endothelium in the omentum and pleura mediastini is very great indeed, and 
hence these membranes play an important part in the generation of lymph- and colour- 

less blood-corpuscles. 

Besides these last-named membranes, there are others which contain germinating 

E 2 



22 



ATLAS OF HISTOLOGY. 



endothelial cells. The peritoneal surface of the diaphragm — especially the central 

tendon contains broader or narrower streaks of small endothelial cells, and amongst 

these there are germinating endothelial cells arranged around the stomata (Klein), i.e. the 
openings by means of which the lymphatics of the diaphragm communicate with the 
peritonea] cavity (see below). In the frog's mesentery, mesogastrium, and septum 
cisternal lymphaticae magnae, there are also isolated or groups of germinating endo- 
thelial cells amongst the ordinary large flat transparent cells. In female individuals 
these germinating cells are ciliated, being possessed on their free surface of a bundle of 
fine hairs. This is especially the case about the spawning time (Dogiel and Schweigger- 
Seidel). On the peritoneal surface of the septum cisternal lymphaticae magnse — the large 
lymphatic cavity extending on each side along the vertebral column and behind the 
peritoneum of the whole abdominal cavity — we find in some frogs, amongst the ordinary 
large fiat cells, continuous and anastomosing streaks, composed entirely of the small 
polyhedral granular, i.e. germinating endothelial cells, which in females during the 
spawning season are all ciliated. As will be pointed out presently, the septum cisternse 
lymphaticae magnae is perforated by numerous holes — by means of these an open 
communication is established between the peritoneal cavity and the clsterna lymph. 
— which in many instances are surrounded by a special layer of germinating 
endothelial cells. These are ciliated in females about the spring and are possessed 
of contractility ; in consequence of this they are able to influence the state of dilatation 
of the stomata which they surround. 

Similar contractility may be noticed under suitable conditions also on some ger- 
minating endothelial cells of the mesogastrium and the mesentery of frog. 



PLATE V. 



All figures, except fig. IV., are drawn under a magnifying power of about 350; 
fig. IV. about 500. 

The brown tint in many figures of this and the following two plates is owing to 
their respective preparations having been stained in nitrate of silver. 

Fig. I. Surface view of the endothelium covering the mesentery of cat. The 
mesentery had been first stained in nitrate of silver, and then in hsematoxylin ; by the 
first process, the outlines only of the endothelial cells, i.e. the interstitial cement-sub- 
stance, is shown, the cell-substance being marked by a uniform brown tint ; by the 
second process the oval and excentric nuclei of the individual cells are brought out in 
addition. 



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ENDOTHELIUM OE FENESTRATED MEMBRANE. 23 

Fig. II. Part of a plexus of connective-tissue bundles from the fenestrated omen- 
tum— stained in carmine — of a rat. The omentum of many mammals— dog, cat, 
guinea-pig, rat, mouse, man — is, in the adult individual, a plexus of broader and narrower 
trabecular, composed of bundles of connective-tissue fibres. These trabecular are 
covered with, or ensheathed in endothelium, the meshes between the bundles beino- left 
entirely uncovered, as represented in figure V. Such a membrane is called a fenestrated 
membrane, and is present in other organs besides the omentum ; e.g. the pleura mediastini 
of many mammals, the mesogastrium of frog, the fenestrated membranes of the liga- 
mentum denticulatum of the spinal cord, and of the ligamentum pectinatum iridis, &c. 
Endothelial cells of these and similar organs, e.g. surface of tendon, outer surface of nerve 
trunks, or blood-vessels that pass through a lymph-sac, are in so far different from those 
of a flat surface, e.g. mesentery, as the endothelial cells constituting the ensheathing 
endothelial membrane are curved, this latter adapting itself to the more or less curved 
surface of the respective organs. 

The same holds good also for the endothelial cells that line a tube, e.g. blood 
vessels and lymphatic vessels. 

In the present figure II. the ensheathing endothelium is recognisable only in 
profile, i.e. on the edges of the trabecular ; the substance of the endothelium being quite 
transparent, it is not noticeable on the surface of the trabecular. 

Fig. III. Surface view of the endothelium covering the peritoneal side of the 
central tendon of the diaphragm. The preparation being stained in nitrate of silver, 
we find only the intercellular cement-substance, i.e. the cell-outlines, represented. 

a. Narrow streaks of small endothelial cells. 

b. Broader streaks of large endothelial cells. 

The membrane (peritoneum) on which the latter (5) are situated covers the tendon 
bundles themselves, whereas that corresponding to the former (a) covers the inter- 
fascicular lymph-channels (see chapter on Lymphatics). 

Fig. IV. Two endothelial plates of mesentery of newt, stained with picrocarmine. 
Each endothelial plate contains in a hyaline slightly stained ground-plate a plexus of 
fine fibre-bundles — intracellular network — in connection with the intranuclear network. 

Fio\ V. Fenestrated omentum. Only the outlines of the endothelial cells (not 
their nuclei) ensheathing the trabecular are shown. 

Fig. VIa. Surface view of endothelium covering the peritoneal side of the frog's 
septum cisternar lymph, magn. The germinating endothelial cells bordering the 
stomata are well shown. Some of these are widely distended, others are quite 

collapsed. 

Fig. VI b. Surface view of the endothelium of the cisternal side of the same 



24 ATLAS OF HISTOLOGY. 

membrane. The character of the endothelium is quite different from that of the 

peritoneal side. The germinating cells surrounding the stomata, especially the open 

ones, are well shown. Copied from Klein's ( Anatomy of the Lymphatic System/ Part I. 

Fig. VII. The endothelium of the same membrane more intensely stained with 

nitrate of silver. In a, seen from the peritoneal ; in b, from the cisternal side. The 

substance of the individual endothelial plates is indicated as a brownish granular matter, 

the nucleus being left clear ; especially well shown in b. This need not necessarily mean 

that the cell-substance has actually become stained by the nitrate of silver and the 

nucleus not, for it is quite possible that the brown matter is a precipitation in the serous 

fluid of the surface only ; owing to its greater thickness, the nucleus projects beyond the 

general surface of the cell, and this part of the surface retains therefore least of that 

serous fluid, and hence contains least of the precipitation. 

The intercellular cement-substance of a contains a uniform precipitation of large 
and distinct granules. 

The outlines of the endothelial cells of b are very sinuous. The same endothelium 
is found on the membranes lining the subcutaneous lymph-sacs of frog. 



PLATE VI. 

Figs. I. II. V. VI. drawn under a magnifying power of about 300; figs. III. 
and IV. under one of about 450. 

Figs. I. II. III. and IV. are copied from Klein's 'Anatomy of the Lymphatic 
System,' Part I. 

Fig. I. Germinating endothelium covering nodules and cords freely projecting over 
the surface of the fenestrated pleura mediastini of a healthy cat. 

Fig. II. Part of an opaque patch and its surrounding of the omentum of rabbit. 

a. Ordinary transparent flattened endothelium. 

b. Opaque patch covered with germinating endothelial cells. Amongst them 
many minute openings — stomata— leading into subjacent lymph-spaces. 

Fig. III. Portion of fenestrated omentum (guinea-pig) in chronic inflammation. 

a. Connective-tissue trabecule covered with ordinary flat endothelium, marked 
here by its outlines. 

b. Trabecular covered with richly germinating endothelial cells. 

Fig. IV. From the mesentery of frog. 

f. Ground substance not represented. 

a. Capillary blood-vessels containing a few blood-corpuscles. Each of these 



ATLAS or HISTOLOGY. ■■ 



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ENDOTHELIUM OF VESSELS. « 

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vessels is a simple endothelial membrane, rolled into a tube. The outlines only— i.e. 
the cement-substance— of the endothelial cells are shown ; these (cells) are very elongated 
plates. 

6. Lymphatic vessels, containing numerous lymph-corpuscles of different sizes. 
The wall of the lymphatic is also made up of only a single layer of endothelial plates, 
more or less polyhedral in shape. In this drawing only the upper wall of the lymphatics 
is represented. 

Fig. V. Plexus of lymphatic tubes of the diaphragm of dog. Their wall is a 
single layer of elongated endothelial plates ; only the upper wall of the vessels is 
represented. 

At v. semilunar valves are seen in profile, their broad surface beino- directed 
towards the lumen of the vessel. Corresponding to the valves, the vessels are 
possessed of saccular dilatations. 

The tissue in which the lymphatics are embedded is marked by a brown tint in this 
and the next figure. 

Fig. VI. Lymphatic capillaries from the diaphragm of rabbit. 

The endothelial plates are less elongated than in the lymphatic tubes possessed of 
valves, like those of fig. V., and show a very sinuous outline. 

In addition to the endothelium described in the foregoing, the basement membrane 
is to be mentioned, which in many mucous membranes separates the epithelium of the 
surface from the subjacent connective tissue of the mucosa. This membrane is not 
homogeneous, but being an endothelial membrane — the subepithelial endothelium, first 
described by Debove of the bladder, bronchi and intestine — is composed of flattened 
nucleated cells, the shape of which varies in different organs, being in some places 
polyhedral, in others more elongated cells, with straight or sinuous outlines. 

The membrana propria of the ducts of some glands, e.g. sweat glands (Czerny), fa 
also a membrane composed of a single layer of endothelial plates. 



26 ATLAS OF HISTOLOGY. 



CHAPTER IV. 

CONNECTIVE- TISSUE CORPUSCLES. 

The r*reat bulk of tissue which for many organs— glands, nerve trunks, vessels, 
muscle, &c— serves as the supporting and connecting substance, while in others, — serous 
and synovial membranes, tendons and fasciae, skin and mucous membranes,— it forms 
the ground-substance, is composed of what is ordinarily called common or fibrous- 
connective tissue. With elastic tissue, cartilage, and bone, it represents the great group 
of ' connective tissues,' all these being in morphological and histogenetical respects 
intimately connected with one another. 

In the present chapter we shall have to deal only with the cellular elements found 
in fibrous connective tissue. They are of two kinds : A. migratory or wandering 
connective-tissue cells (v. Recklinghausen), and B. fixed connective-tissue cells, or 
connective-tissue corpuscles par excellence. 

A. The migratory connective-tissue cells are the amceboid cells found in fibrous 
connective-tissue ; they are protoplasmic cells, just like colourless blood-corpuscles, with 
one, two, or three nuclei ; they also resemble them in size. In connective-tissue of 
loose arrangement, e.g. subcutaneous and submucous tissue, they are more numerous 
than in parts of a denser structure. They are found more numerous in connective 
tissue which is richly supplied with blood-vessels, e.g. the connective-tissue in and 
around glands and muscle. In the superficial parts of the corium and mucosa and the 
cornea, they are found more often than in the deeper parts of these organs. Under 
inflammatory conditions the connective-tissue contains great numbers of migratory cells 
—pus cells,— many of which are however derived from colourless blood-corpuscles that 
have emigrated from the vessels (Cohnheim). But of course it is impossible to 
distinguish the one from the other. 

If pigment matter, such as vermilion or carmine, is injected into the circulating 
blood in a finely divided state, some pigment granules are taken up by colourless blood- 
corpuscles, others not, and these may find their way into the connective-tissue of different 
regions, being carried through the wall of the capillary vessels by the natural current 
that passes from the latter into the surrounding tissue ; here they (pigment granules) may 
be taken up by migratory connective-tissue cells and through these may be distributed 
to distant regions. But the pigment-granules may be carried through the walls of 



MIGRATORY CONNECTIVE-TISSUE CELLS. 27 

the capillary vessels by means of the colourless blood-corpuscles that had swallowed 
them within the vessels. Having left the blood-vessel, these cells migrate about in the 
surrounding connective tissue, and, as has been mentioned in Chapter I., may during 
this time gradually eject and leave behind their load of pigment granules. These may 
be swallowed again by migratory connective-tissue cells, which have had no immediate 
connection whatever with the capillary vessels. If, then, we inject carmine into 
the circulating blood of a frog, and we produce an inflammation in some connective 
tissue— e.g. tongue, or cornea, or web of foot, and we find in the inflamed part many 
migratory cells— pus cells— containing carmine granules, we are not justified in con- 
cluding that these cells are all colourless blood-corpuscles that have emigrated from the 
vessels, for the pigment granules contained in them are no index of their origin. The 
pigment granules may have been imported into the inflamed part by migratory con- 
nective-tissue cells that found them in the connective-tissue whither they were carried 
by other agencies (Strieker). 

In addition to the migratory cells, as described above, there exist other corpuscles 
which show only very slight amoeboid movement, are larger than the ordinary migratory 
cells, contain a single relatively large nucleus, are unbranched, and, in many instances, 
contain real granules which stain very markedly deep blue in hematoxylin, and become 
hereby very conspicuous. They are to be found in the vicinity of small blood-vessels, 
in the serous membranes, submucous tissue, in the connective-tissue sheath of nerve 
trunks, in the trabecular of lymphatic glands, in the intermuscular tissue of tongue, and 
in the intermuscular connective tissue in general. These corpuscles correspond to the 
plasma-cells of Waldeyer, and have been noticed by many previous observers. 

B. The fixed or connective-tissue corpuscles proper are transparent, more or less 
elastic, and flattened nucleated cells, which bear a definite relation to the connective- 
tissue ground-substance in which they are situated. 

The connective-tissue ground-substance is in most instances composed of larger or 
smaller cylindrical or bandlike bundles of minute fibrils, and it is the peculiar arrange- 
ment of these bundles which determines the shape and nature of the connective-tissue 
corpuscles. 

In tendon and in kindred connective tissue (fascia, aponeurosis) the bundles are 
arranged parallel with each other, and they form groups. Between each two groups 
we find a more or less straight channel— interfascicular lymph-channel ; in these channels 
lie the connective-tissue cells, forming for each such channel a single continuous row of 
flattened cell-plates— the so-called tendon cells (Ranvier). This row of cell-plates 
covers only a section of the circumference of the channel (the other section being left 
uncovered), and in doing so the cell-plates have to adapt themselves to the more or less 

F 



2 S ATLAS OF HISTOLOGY. 

curved surface of the tendon-bundles which surround the channel. Generally five to 
eight (sometimes even less) bundles surround, or rather form, the channel by joining 
into one group, and of the free surface of these— i.e. the surface forming part of the 
boundary of the channel — only two or three are covered with the row of the cell-plates, 
so that each of these cell-plates is correspondingly composed of two or respectively 
three concave sections, which join in a straight ridge, single in the former, double in 
the latter case (elastic stripe or stripes of Boll). The cell being flattened, a transverse 
section shows either two slightly curved lines joining in a projecting ridge, or two such 
lines joined by a middle horizontal line, also concave. In this latter instance we have 
to do with a cell-plate possessed on each side with a winglike expansion (Griinhagen). 

The shape of these tendon-cells is more or less oblong, each being separated from 
its neighbour at each end by a linear cement-substance. But laterally the cell-plates 
are possessed of fine processes extending into the depth. These processes are better 
seen in cells of adult than in those of young tendon. 

In the skin, mucous membranes, and similar organs, the connective-tissue bundles 
cross each other in groups or singly, and are at the same time branched, and exchange 
fibrils with their neighbours : in this way a very complex system of spaces is formed 
between the groups of bundles. These spaces — interfascicular spaces — vary in size 
according to the looseness or density of arrangement of the bundles, and contain the 
connective-tissue corpuscles, which are flattened nucleated cells possessed of more or 
less branched processes. As in tendon so also here the cell-plate is of a complex 
nature, being possessed of two or more membranous projections according to the cell- 
plate covering the breadth of several bundles, and sending between them membranous 
projections. Generally there is one section of the cell-plate which is the largest, and 
which usually contains the nucleus. This is the chief plate, whereas the other smaller ones 
coming off from it under various angles are the secondary plates (Waldeyer). All 
these membranous parts of the cell-plate are drawn out into fine processes, which vary 
considerably in length, and which often are again branched and connected with each other. 
In the serous membranes, synovial membranes, and other similar membranous or 
lamellar expansions of connective tissue, the connective-tissue corpuscles are likewise 
flattened nucleated cells possessed of processes more or less branched and connected 
with each other. The cells expanding prominently in a level parallel to the surface of 
the membrane, there is not much chance of their being possessed of chief and secondary 
plates ; each cell being a plate from which processes — some filamentous, others mem- 
branous — come off chiefly in the level of the cell-plate. But there are in some instances 
more or less distinct indications of membranous processes passing upwards or downwards 
in a more or less vertical direction. The same applies also to the cornea ; here the 
connective tissue possesses a distinct lamellar arrangement, and the connective-tissue 



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STRUCTURE OF CONNECTIVE-TISSUE CELLS. 29 

corpuscles are found to expand chiefly between the lamellce in a horizontal manner, 
but there are also such cells as are arranged obliquely, or even vertically, to the 
general direction of the lamellae (Rollett). 

In the case of cornea, serous membranes, and other membranous expansions 
of connective tissue, e.g. the connective-tissue lamellae that can be obtained from the 
subcutaneous or submucous tissue, it can be shown that each connective-tissue corpuscle 

is composed of two distinct substances (Klein) : (a) a hyaline plate — ground-plate which 

contains the oval nucleus, the substance of which is a dense network — intranuclear 
network ; and (b) a second substance — a network of minute fibrils, intracellular network 
— arranged always more copiously at one side of the nucleus than at the other, and 
extending from here beyond the limits of the ground-plate, as finer or thicker branched 
or unbranched processes. This second substance is in connection with the intranuclear 
network. The ground-plate extends only on the more membranous processes. 

It is probable that also in the case of the connective-tissue cells possessed of a chief 
plate and secondary plates with fine filamentous processes, we have to distinguish the 
hyaline substance containing the nucleus from the network of minute fibrils extending 
beyond the limits of both chief and secondary plates ; the difference being only that 
here the ground-plate is not a single flat plate, as is the case in the serous membranes, 
but sends off under different angles several other plates — secondary plates. 

The ' granular ' appearance of the connective-tissue cells is due to the density of 
the intracellular network. The branched nucleated corpuscles, entirely composed of 
'granular' protoplasm, as they represent themselves under various conditions, are only 
one part of the corpuscle, viz. the nucleus and the surrounding network of fibrils, i.e. 
substance b mentioned above, the hyaline ground-plate not being then perceptible. 
Whereas the representation of connective-tissue corpuscles as hyaline unbranched plates 
with an oval nucleus refers also only to one part of the connective-tissue corpuscle, viz. 
nucleus and the ground-plate, i.e. substance a mentioned above. 

PLATE VII. 

Figures I. II. and IV. drawn with a magnifying power of about 450 ; the other 
figures with one of about 350. 

Fig. I. A portion of fenestrated omentum of adult guinea-pig. The omentum 
had been stained first in nitrate of silver and then in logwood. The plexus of connec- 
tive bundles forming the fenestrations is stained faintly in hematoxylin ; it is covered on 
both surfaces with endothelium, as mentioned on a former occasion ; the nuclei of the 
endothelial cells are brought out very well, and contain a uniform dense network. The 

F 2 



,2 ATLAS OF HISTOLOGY. 



It is also noticed in this fieure that the interfascicular channels are flatter near the 
surface of the tendons than in the depth. 

PLATE VIII. 

All figures of this plate, except fig. XV., are drawn under a magnifying power of 
about 450; fig. XV. about 350. 

Fig. VIII, Three connective-tissue corpuscles of mesentery of newt, prepared first 
with chromate of ammonia and then with carmine. The distinction between the two 
substances, viz. hyaline ground-plate and intracellular network of fibrils, is very clear. 
The latter substance forms a larger or smaller accumulation at one side of the nucleus, 
with the network of which it is intimately connected, and is drawn out into the longer 
or shorter branched processes. Some of these resemble, at one point or other, 
membranous, not filamentous expansions. 

Fig. IX. Vertical section through perichondrium and hyaline cartilage stained first 
with chloride of gold and then in logwood. 

a. Loose connective tissue around perichondrium ; the thin bundles of connective- 
tissue fibres leave between them relatively large spaces containing the connective-tissue 
cells ; in most of them only the nucleus is brought out. 

b. Perichondrium, composed of connective-tissue bundles ; most of these being 
arranged longitudinally — especially in the right part of the figure — are all cut transversely. 
It is seen that here, just as in tendon, exist large spaces — interfascicular lymph- 
spaces — between groups of connective-tissue bundles ; in these spaces lie the connective- 
tissue cells (their nucleus being shown here only) ; the small spaces passing from the 
large interfascicular spaces between the individual bundles contain the cement-substance 
uniting contisfuous bundles. 

c. Hyaline cartilage ground-substance containing the nucleated cartilage-cells. 
Fig. X. From a preparation of the tail of tadpole, stained with chloride of gold 

and logwood. 

m. Two migratory connective-tissue cells ; the other cells are the ordinary branched 
cells, each with an oblong nucleus. Many of the processes of these corpuscles are not 
filamentous, but membranous : this is, however, not brought out well in the figure. 

Fig. XI. Corneal corpuscles — viewed from the surface — of frog ; chloride of gold 
specimen. 

Fig. XII. The same of kitten; chloride of gold specimen. The distinction that 
had been pointed out in figs. VI. and VII. is also observable in these two figs. XL and 
XII. ; viz. that in frog the corneal corpuscles are more isolated than in kitten, they 
being here in many places grouped together. 









pj vm 







• 



m 










A 



•*> 






i 






.-o 



VII 



IX 



* 



<»#•* 











■ 


f 1 
/ 1 



XI 



■ 



«s 



|§j 



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• .v', 1. 



A * 



V r 












■ 



CORNEAL CORPUSCLES. 33 

In fig. XI. the substance of the corneal corpuscles is less stained than the nucleus 
or nuclei. The cornea had been slightly inflamed and we find many corpuscles 
possessing two nuclei, the originally single nucleus having undergone division. 
In fig. XII. the nucleus is transparent as compared with the cell-substance. 
If we compare these two figs. XI. and XII. with figs. VI. and VII., we have to 
regard the former as the positive images of the latter, i.e. the negatives ; the former being 
the cells themselves, brought out by chloride of gold, occupy the spaces, i.e. the lymph- 
canalicular system of the latter, brought out by nitrate of silver. But it will be noticed 
that the corpuscles brought out by chloride of gold do not, as regards size, completely 
coincide with the lacunar system brought out by nitrate of silver. The very same 
difference may be shown to exist when comparing the lacunar system of a silver- 
preparation of mesentery — the surface-endothelium having been pencilled off before 
staining with silver — with the network of branched corpuscles of a gold specimen of the 
same membrane, viz. the latter is much smaller than the former. The explanation of 
this is very simple, it has been given above: in chloride of gold specimens we miss the 
ground-plate (see fig. VIII.), and we see only the nucleus with the substance that we 
called previously the intracellular network of fibrils. 

Fig. XIII. From a vertical section through the tissue of cornea, hardened in 
bichromate of potash and stained in logwood. 

The ground-substance is composed of bundles of fibrillar connective tissue. Between 
groups of bundles we see the interfascicular, or rather interlamellar lymph-spaces ; these 
are viewed here in profile, the cornea being cut vertically, and the lymph-spaces, i.e. the 
lacunar system, having, as mentioned above, an expansion parallel to the surfa.ce of 
the lamellae. The lacunae of the lymph-canalicular system are represented here as 
large, widely-distended spaces, the canals by means of which they anastomose (see figs. 
VI. and VII.) are (except in two or three instances) not shown here for obvious reasons. 
A section placed vertically on figs. VI. and VII., and then viewed sideways, would 
only in very few instances show the canals connecting neighbouring lacunae. 

In our vertical section, fig. X1IL, the lacunae are abnormally distended, and in 
them are seen, in profile, the flattened nucleated corneal corpuscles ; in some lacunae we 
see in addition one or two round nuclei belonging to migratory cells. 

As in the case of tendon and other connective tissues, so also in the cornea the 
interfascicular lacunar system contains, besides the connective-tissue cells, also the 
irrio-atino- albuminous fluid-plasma ; and this lacunar system represents at the same 
time the passages through which the amoeboid corpuscles find their way. 

Fig. XIV. From a transverse section through the external part of cedematous skin. 
a. Lymphatic vessels lined with endothelium, seen here in profile, b is a section 
through a valve of a lymphatic. The ground-substance of the skin is composed of 



34 ATLAS OF HISTOLOGY. 

connective-tissue bundles cut in different directions, some longitudinally, others obliquely, 
and many others transversely, this being due to the fact that in the upper part of the 
skin the connective-tissue bundles cross each other in all different directions. The 
flattened connective-tissue corpuscles are seen here mostly in profile as spindle-shaped 
or angular corpuscles. The cause of this latter appearance has been explained above, 
viz. the corpuscles are composed of two or three plates (chief and secondary plates, 
Waldeyer) according to whether they have to adapt themselves to the surface of two or 
three bundles. Now, the difference between a section through ordinary normal skin or 
mucous membrane and one through cedematous skin or mucous membrane is very 
conspicuous. It is this : in a section through ordinary skin the lymphatic vessels are 
generally difficult to recognise, being found collapsed, whereas in oedema they are 
distended by the excessive amount of exuded plasma and are therefore easier discernible. 
And further, in ordinary skin or mucous membrane, as in other connective tissues, the 
bundles are arranged in groups, and between them we find the interfascicular lymph-spaces 
intercommunicating with each other; in cedematous skin or mucous membrane we 
find the lymph-spaces extending between almost all individual bundles, the excessive 
amount of plasma present in the tissue having separated these from one another. 

The cedema is usually, especially if of some duration, associated with emigration of 
colourless blood-corpuscles from the minute blood-vessels, and these (corpuscles) pass 
through the interfascicular lymph-spaces into the lymphatic vessels. But when, e.g. in 
acute inflammation, the migratory cells accumulate in too great numbers in these spaces 
—infiltration of the tissue with pus-corpuscles,— the connective-tissue bundles having 
become destroyed, the interfascicular spaces become all confluent, and in this way an 

abscess is formed. 

In this figure XIV. the direct and open connection of the interfascicular lymph- 
spaces with the lymphatic vessels is clearly shown, and hence also the unity of the 
endothelial cells lining the lymphatic vessels and the connective-tissue corpuscles 
situated in the interfascicular lymph-spaces. 

Fig. XIV. From the omentum of a rat, stained with logwood, showing con- 
nective-tissue bundles of various sizes anastomosing with each other ; numerous nucleated 
spindle-shaped-looking c^lls— endothelial cells and connective-tissue cells viewed in 
profile; a capillary blood-vessel showing the nucleated endothelial membrane forming its 
wall ; several large coarsely granular cells, each with a large clear nucleus. These last- 
named cells correspond to the plasma-cells of Waldeyer ; in the omentum of rat and 
mouse they become converted into fat-cells. 

The membrana propria of the alveoli of secreting glands, e.g. lacrymal-, mucous-, 
salivary-, and other glands, is a network of nucleated, branched, and flattened connective- 
tissue cells (Boll, v. Ebner, Watney, and others). 



03 



CHAPTER V. 
FIBROUS-CONNECTIVE TISSUE. 



The fibrous-connective tissue or white fibrous tissue has a very great distribution, as 
has been mentioned in the preceding chapter. It consists of more or less cylindrical 
bundles of different sizes ; these, being arranged in smaller or larger groups, form 
broader or narrower trabecule. The bundles are generally more or less wavy, but this 
depends in a great measure on the state of contraction or expansion of the respective 
tissue of which they form part. Each bundle is composed of minute homogeneous 



Errata. 



the Explanation to Plate VI. of Tart II. (pp. 


24 and 


25) 


for Fig. I. 


read 


Fig. VIII, 


„ Fig. n. 


,- 


Fig. IX. 


,, Fig. III. 


M 


Fig. X. 


„ Fig. IV. 


.. 


Fig. XI. 


,, Fig. V. 


M 


Fig. XII. 


„ Fig. VI. 


> » 


Fig. XIII. 



*^ n P- 3 I >/<"'Fig. IV. Transverse section read Fig. V. Transverse ■■eclion. 



It has been mentioned in the preceding chapter that in many instances the con- 
nective-tissue bundles branch and anastomose. The branching means a division of a 
large group of fibrils into smaller groups, but not a division of the elementary fibrils ; 
the anastomosing is due to an aggregation of two or more small bundles into one, but 
not to an anastomosis of the primitive fibrils. (See fig. XV. of Plate VIII.) 
The fibrous bundles of connective tissue are arranged in various ways : 
a) As fenestrated membranes, in the omentum and pleura mediastini of 
mammals, ligamentum pectinatum iridis, ligamentum denticulatum of spinal cord 
and the subarachnoidal tissue ; here the bundles form lamellar expansions com- 
posed of larger or smaller trabecular which branch and again reunite with one 

another. 

G 



34 ATLAS OF HISTOLOGY. 

connective-tissue bundles cut in different directions, some longitudinally, others obliquely, 
and many others transversely, this being due to the fact that in the upper part of the 
skin the connective-tissue bundles cross each other in all different directions. The 
flattened connective-tissue corpuscles are seen here mostly in profile as spindle-shaped 
or angular corpuscles. The cause of this latter appearance has been explained above, 
viz. the corpuscles are composed of two or three plates (chief and secondary plates, 
Waldeyer) according to whether they have to adapt themselves to the surface of two or 
three bundles. Now, the difference between a section through ordinary normal skin or 
mucous membrane and one through (Edematous skin or mucous membrane is very 
conspicuous. It is this : in a section through ordinary skin the lymphatic vessels are 
generally difficult to recognise, being found collapsed, whereas in cedema they are 
distended by the excessive amount of exuded plasma and are therefore easier discernible. 
And further, in ordinary skin or mucous membrane, as in other connective tissues, the 



ji 



j i- 



.V 




endothelial cells lining tne 

situated in the interfascicular lymph-spaces. 

Fig. XIV. From the omentum of a rat, stained with logwood, showing con- 
nective-tissue bundles of various sizes anastomosing with each other ; numerous nucleated 
spindle-shaped-looking cells-endothelial cells and connective-tissue cells viewed in 
profile; a capillary blood-vessel showing the nucleated endothelial membrane forming its 
wall ; several large coarsely granular cells, each with a large clear nucleus. These last- 
named cells correspond to the plasma-cells of Waldeyer; in the omentum of rat and 
mouse they become converted into fat-cells. 

The membrana propria of the alveoli of secreting glands, e.g. lacrymal-, mucous-, 
salivary-, and other glands, is a network of nucleated, branched, and flattened connective- 
tissue cells (Boll, v. Ebner, Watney, and others). 



35 



CHAPTER V. 
FIBROUS-CONNECTIVE TISSUE. 

The fibrous-connective tissue or white fibrous tissue has a very great distribution, as 
has been mentioned in the preceding chapter. It consists of more or less cylindrical 
bundles of different sizes ; these, being arranged in smaller or larger groups, form 
broader or narrower trabecular The bundles are generally more or less wavy, but this 
depends in a great measure on the state of contraction or expansion of the respective 
tissue of which they form part. Each bundle is composed of minute homogeneous 
fibrils, elementary fibrils. These are held together, within the bundle, by an albu- 
minous and homogeneous cement-substance. By dissolving this the fibrils become 
distinct and isolated; permanganate of potash (Rollett), lime-water or baryta water, 
especially a 10 per cent, solution of chloride of sodium (Schweigger-Seidel), are used for 
this purpose. 

The elementary fibrils swell up to a great extent in acids and alkalies, and after 
boiling. Hereby the bundles lose their fibrillar appearance and become more homo- 
geneous. This effect is produced on account of the fibrils containing a substance which 
by boiling and dilute acids is converted into glutin or gelatin. 

In many connective-tissue organs, as in tendon, fascia, subcutaneous tissue, sub- 
arachnoidal tissue, &c, the bundles are surrounded by a more or less complete hyaline 
elastic sheath. When therefore these bundles are treated with acids, i.e. are made to 
swell up, they show more or less numerous annular constrictions. 

It has been mentioned in the preceding chapter that in many instances the con- 
nective-tissue bundles branch and anastomose. The branching means a division of a 
large group of fibrils into smaller groups, but not a division of the elementary fibrils ; 
the anastomosing is due to an aggregation of two or more small bundles into one, but 
not to an anastomosis of the primitive fibrils. (See fig. XV. of Plate VIII.) 

The fibrous bundles of connective tissue are arranged in various ways : 

a) As fenestrated membranes, in the omentum and pleura mediastini of 
mammals, ligamentum pectinatum iridis, Iigamentum denticulatum of spinal cord 
and the subarachnoidal tissue ; here the bundles form lamellar expansions com- 
posed of larger or smaller trabecule, which branch and again reunite with one 
another. 

G 



d 



6 ATLAS OF HISTOLOGY. 



6) Or, the bundles are arranged in parallel groups, as in tendons, ligaments 
and fascia? ; in the latter the lamellae of parallel bundles may cross each other under 
various angles. To this category belongs also the cornea, although bundles of one 
lamella anastomose with those of the next upper or lower one. 

c) In the loose cellular tissue, such as subcutaneous-, submucous- and intermuscular 
tissue, or in the connective tissue around vessels, nerves and glands, &c, the connective- 
tissue bundles are arranged as smaller or larger trabecular which branch and anastomose 
with one another, and crossing each other in more than one direction, they leave between 
them spaces of relatively considerable size, — the 'cells' of gross anatomists; and 
hereby the tissue possesses a certain loose and spongy structure. These spaces belong 
to the lymphatic system, as will be described in detail in a future chapter. By the 
injection of air, mercury, water or other fluids, or warm (fluid) gelatine (Ranvier) 
into this tissue, its bulk becomes of course enlarged, but the enlargement is uniform, 
owing to the air or fluids being able to spread into all its spaces (' cells '), these intercom- 
municating with each other. In cedema it is chiefly such loose connective tissue that 
swells up by the exuded plasma to a greater extent than other parts. 

d) Dense connective tissue, as in skin, mucous membranes, many serous-, synovial- 
and kindred membranes, and dura mater, contains bundles of fibrous tissue very 
closely arranged, these being much branched and crossing each other in all different 
directions. In this manner a dense feltwork is produced. In serous- and synovial 
membranes, as well as in the dura mater, there are, however, parts, especially in the 
immediate neighbourhood of the large vessels, where the connective-tissue bundles 
possess a parallel arrangement. 



In combination with fibrous-connective tissue we always find a greater or less 
amount of elastic tissue (yellow elastic tissue). This tissue differs in morphological and 
chemical respects from fibrous-connective tissue : elastic-tissue fibrils do not as a 
rule form bundles like the fibrils of fibrous-connective tissue ; they are branched and 
anastomose with each other so as to form a real network ; they do not swell up, but 
remain unaltered by boiling, acids or alkalies, and do not yield glutin but elastin ; when 
torn they curl up at their ends. 

The arrangement and distribution of elastic fibres is this: — 

i) They are fine homogeneous and sharply outlined fibrils branching and anasto- 
mosing with each other in a network ; the network is in some places close, in others very 
open, owing to the richness or scarcity of the number of the fibrils and their branches ; 
the fibrils are straight or they are very wavy and twisted, but this depends in a great 



ELASTIC TISSUE. 

.neasure on the ante of c„„, r ac,i„„ or expansion of , he ^ .„ ^ 

coined. Or *. cha.ac.e. « nnd , he Cas.ic .issue i„ .„, sti „ and muc0 „ s „_££ 

subcutaneous and submucous .issue, serous, synovial- and Kindred m e m b r a„es ,he ZT 

he loose „»„ KB ve tlsSM separali „ g „ co »*£» 

termuscular connective tissue Th„ „, * • r . . 

e matnx of elastic car tilage and the bulk of the 
mucosaof the true voca, cords (human) are ma de up of networks of these fibri.s an , 
n. the coa s of arteries and veins we find this f orm of elastic tissue, but not so 'abund 
as other forms (see below). The relation of the network of elastic nbri, n ma n 
connects t-ssues ls th, s: the elastic fibrils are situate on ^ ^ ™> 

the connecuve-t.ssue bundles, and in close proximity t0 the ^^J^ 
covering the bundles (Axel Key and Retzius). 

2) Thick, cylindrical or bandlike, solid, sharply outlined homogeneous fibres branch- 
mg andanastomosmg into a network. They are present, in addition to those ment on 
before in the skin and mucous membranes, e.g. mouth and pharynx. In the inner 

Tall 77/ th£ traCHea ^ ^ br ° nChi ^^ *"* in ™ with a 

mall amount of fibrous-connective tissue, a special longitudinal layer. They obtain 

then-greatest development in vellow ligaments, e.g. ,i gamentum nucn£E of [ , iga . 
men a fiava, & c, here they form the chief constituents, containing only a small amount 
of fibrous-connective t.ssue with the ordinary connective-tissue corpuscle, They are 
broader or narrower cylindrical or bandlike fibres richly branched and anastomosing the 
fibres with their branches are arranged longitudinally, so that at first sight the tissue 
appears composed of parallel fibres ; but in a thin section, especially when pulled out 
transversely, the branching and anastomosing of the fibres can be easily ascertained By 
prolonged treatment with strong solutions of caustic potash Schwalbe has demonstrated 
that these fibres possess a thin sheath. 

In larger blood-vessels, especially arteries, they obtain a great development. (See 
a later chapter.) 

3) Perforated elastic membranes (membrana fenestrata, Henle) ; these result 
from the individual elastic fibres being very broad and anastomosing into a net- 
work with few and small meshes. Of this nature is the elastic tissue in arteries (intima 
and med.a), and also veins (media), as will be mentioned in the chapter on Blood- 
vessels. 

4) Continuous elastic membranes. These membranes possess all the chemical 
characters of elastic tissue ; they appear in many instances homogeneous, but under 
suitable conditions can be shown to contain bundles of minute fibrils. To this form of 
elastic tissue belong : 

a) The anterior elastic membrane (Bowman) of the human cornea, situated im- 



. 8 ATLAS OF HISTOLOGY. 

mediately underneath the epithelium of the anterior surface. In the cornea of the 
human eye this membrane is very conspicuous on account of its thickness ; but in 
the cornea of the domestic animals it is of great thinness, and therefore not easily 

perceived. 

6) The posterior elastic membrane of the cornea (membrana Descemeti) ; this mem- 
brane is on account of its great thickness everywhere easily perceptible ; it appears quite 
homogeneous, but with the aid of a 10 per cent, solution of chloride of sodium bundles 
of minute fibrils can be demonstrated in it (Schweigger-Seidel). 

c) Similar in structure is the subendothelial hyaline layer of the human serous 
membranes described by Bizzozero. 

d) The thick homogeneous-looking membrane directly underneath the epithelium, 
lining the mucous membrane of the respiratory organs, especially the human nasal cavity 
(Heiberg), true vocal cords and trachea of man. In all these instances this subepithelial 
elastic membrane is without any nuclei, and contains the anastomosing branches of 
the lymph-passages of the epithelium and mucosa. (See chapter on Lymphatic 

System.) 

A similar thick elastic membrane is present on the outer surface of the mucosa of 
stomach of cat (Zeissl) ; here the membrane is perforated by numerous fibres, blood- 
vessels, muscles, &c, ascending from the tissue underneath into the mucosa. 

Elastic membranes of other organs (capsule of lens, sheath of muscle fibres, 
limitans interna and externa of retina, elastic membranes of Pacinian corpuscles) will be 
mentioned at the respective places. 

The elastic membranes composed of endothelial plates (basement membrane, 
membrania propria of glands) have been mentioned in the preceding chapters. 



Besides the fibrous connective tissue and the elastic tissue, there are other forms of 
connective tissue, in morphological respects closely related to both, although differing 
from them in some essential respects. 

a) The gelatinous tissue (Virchow) present in the foetal umbilical cord in an early 
stage as the so-called Wharton's tissue, the foetal skin, the tissue of foetal tooth-sac, the 
tissue in the rhomboidal sinus of the cord of birds, in the electric organs of fishes, and in 
different localities of other fishes and especially invertebrate animals, the tissue contained 
in the infraorbital fossa of young rabbits, in pathological conditions (myxomatous tumours), 
&c. The gelatinous tissue is a transparent jelly-like substance containing in the meshes of 
a framework a hyaline mucous substance. The tissue varies according to the nature of the 
framework, this being in some instances (early stage of foetal umbilical cord or foetal skin) 



GELATINOUS TISSUE. 39 

a network of cells and their processes ; in the later stages the foetal umbilical cord, 
although still of a gelatinous aspect, contains already numerous bundles of fibrous-con- 
nective tissue ; in other instances it is composed of non-nucleated fibrous bands (fishes 
invertebrate animals, &c), and in a third group it contains, besides cells, blood-vessels and 
bands of connective-tissue fibres, also fat-cells in different states of development. In 
this last instance the gelatinous tissue is the precursor of fat-tissue, as is the case with the 
tissue of the infraorbital fossa of young rabbits and the foetal subcutaneous tissue, and 
therefore, strictly speaking, should not be placed in the same group with the tissues 
mentioned before. 

6) The network of homogeneous fibrils that forms the matrix of the central nervous 
system, including the optic nerve, the so-called neuroglia, will be considered minutely 
in a future chapter. 

c) The reticulum of homogeneous membranes and filaments forming the matrix 
of lymphatic tissue, the so-called adenoid reticulum, will be considered^ detail in 
connection with the lymphatic glands. 

Both neuroglia and adenoid reticulum are in chemical respects neither identical 
with fibrous-connective tissue nor with elastic tissue. 

The reticulated tissue representing the supporting framework in different glandular 
organs, e.g. the reticular tissue between the urinary tubes of cortex of kidney, the 
reticular tissue supporting the liver cells, the reticulum of the pulp of spleen, &c, does 
not form a special group, being a honeycombed structure composed of nucleated, 
membranous, branched, and anastomosing connective-tissue cells. 



Fibrous-connective tissue is developed directly from embryonal connective-tissue 
corpuscles (Max Schultze, Brucke, Obersteiner, and others). These are at first spherical, 
then elongated, spindle-shaped cells with an oval nucleus. Each cell gives origin to 
a bundle of connective-tissue fibres (Breslauer, Boll), the nucleus gradually disappearing. 
But besides this mode of direct transformation of the original protoplasm of the cell into 
a bundle of connective-tissue fibres, there is another mode, consisting first in the 
production of a homogeneous (peripheral) substance by the embryonal cells them- 
selves and subsequent formation of bundles of fibrous tissue in it (Henle, Rollett, 
and others). 

The former, viz. direct mode of formation of bundles of connective-tissue fibres is 
to be observed in tendon, skin, intermuscular tissue, nerve trunks, loose cellular tissue, 
&c. In the umbilical cord and serous membranes there is, besides this, also the other, 
viz. indirect mode of formation. 



40 ATLAS OF HISTOLOGY. 

In various abnormal conditions, as in chronic inflammation, tumours, certain specific 
diseases, &c, new fibrous-connective tissue is being formed in great masses. Its mode 
of formation is the same as in the normal (embryonal) state, being derived either directly 
or indirectly from cellular elements in the manner stated above. 

The elastic fibrils are formed by the direct conversion of nucleated embryonal 

cells and their processes (Henle, Thin). The nucleus is lost as the development 

proceeds. 

The neuroglia and the adenoid reticulum are developed in the same manner by the 

direct conversion of nucleated cells (see later chapters). 



PLATE IX. 

The figures of this Plate are drawn under a magnifying power of about 350. 
Fig. XVI. This figure properly belongs to the chapter illustrated on the preceding 
Plate, for it represents corneal corpuscles of rabbit. The cornea had been inflamed and 
prepared with chloride of gold. In addition to the ordinary branched corneal corpuscles 
we find small cells, each with two or three nuclei ; these cells are (migratory) pus-cells. 
In the figure it is seen that these pus-cells are oblong, and that they are in close 
proximity to the corneal corpuscles. The reason is simply this : the passages through 
which these pus-cells migrate are the same in which the corneal corpuscles are situated, 
viz. the lymph-canalicular system. When a pus- cell has to squeeze itself through a 
canal it must elongate its body ; these canals being at the same time the spaces for the 
processes of the corneal corpuscles (see previous chapter), it follows that many pus- 
corpuscles appear connected with those processes ; in reality they are only above or 
below them, but in the same canal. 

Fig. XVII. (a) A layer of more or less sharply outlined, parallel, and wavy bundles 
of connective-tissue fibrils, from the mesentery of rabbit. On the surface of this layer is 
(6) a network of fine elastic fibres. 

Fig. XVIII. (a) Branching and anastomosing bundles of fibrous-connective tissue. 
(d) Network of fine elastic fibres. From the mesentery of cat. 

Fig. XIX. A bundle of fine connective-tissue fibres (b) ensheathed in an endo- 
thelial membrane (a) seen in profile, (c) Fine elastic fibres ; they are not situated 
within the bundle of connective-tissue fibres, but on the surface of this and underneath 
the endothelium. From the subarachnoidal tissue of man. 

Fig. XX. A portion of elastic lamella, dense network of fibrils, separated by 
teasing from the middle coat of aorta of rabbit, after being acted upon by acetic acid. 






i S - - ^l* 









■ 









I 














































I 1 






ELASTIC TISSUE. 4 i 

Fig. XXI. Network of thick elastic fibres, in a longitudinal section of ligamentum 
nuchse of ox ; the section had been treated with dilute acetic acid. 

Fig. XXII. From a section through ligamentum nuchas of giraffe. The prepa- 
ration had been stained in hematoxylin and then teased out. The elastic fibres are 
here much thicker and bandlike ; they possess within a distinct sheath irregular trans- 
verse thickenings. 



ATLAS OF HISTOLOGY. 
42 



CHAPTER VI. 

ADIPOSE TISSUE. 

t t rrU tissue in its ripe state possesses several characters which place it in 
Apxpose or fat-cell tissue its p P sessed of an afferen t artery, 

son. places embracing only one, in others two or three elementary fat-cells. Th e 
te are arranged by means of connective tissue, in smaller or larger groups, lobules 

r;:: r;^ ^ to — As - — «-«** - ^ - - 

lobe and lobule have their respective branch of artery and vein (or vems). 

The elements of ripe adipose tissue, such as occurs in contmuous masses ,n he 
subculneot s b„ serous, and subserous tissue, in the intermuscular and other 
LoseTllar connective tissue, are the so-called fat-cells ; they are closely aggrega , 

ran be traced between the fat-cells. 

rrsr-nim x«, — - — - me r: 

tissue in wiin. _ becomes richly vasculansed. 

into fat-cells (Flemming) ; increasing in size, this tissue become y 

into tat cens <, „/ fat-tissue is derived from 

in r.tW nlaces e £. serous membranes, the great mass 01 

In other places, e.g. (especially in connection 

a peculiarly changed connective tissue (Klein) , in many 1 v 1 J 

, the large vessels) there appear in the connective-tissue matrix of the serous tnern- 
nepatchs, nodules or cords, which are made up of multiplying «"»«™^ 
A e numb r of the cells increases, the matrix in which they are embed edecome 

As tne num ^ rn „, r les a opear amongst them, and after the tissue 

transformed into a reticulum ; lymph-corpuscles appear d 5 

rtle rich!, vascahtrised by an afferent artery, efferent ve,„ (« ve.ns) and a r, h 
nlTlof canaries,!, resemhfc in morphea, respects lyntphat.c t.ssae. The 



ADIPOSE TISSUE. 

43 

serous membranes of many mammals and man possess in the young and adult state a 
considerable amount of this species of lymphatic tissue. In some animals it is found 
to have a greater development than in others ; in some places it is arranged more in 
the shape of cords or patches, in others more as nodular masses along the larger 
branches of vessels which supply them with their vascular system. The small i e the 
youngest cord, patch, or nodule, does not possess any vascular system, but this soon 
appears as that organ enlarges : first it is represented by a simple capillary loop derived 
either from a neighbouring patch or nodule, or directly from a larger vascular branch ■ 
then numbers of new capillaries are formed either directly in connection with the 
existing capillary vessel, or independently of this, from connective-tissue cells of the 
patch or nodule in a manner which will be described minutely in the chapter on Blood- 
vessels ; one branch of the original capillary loop is changed into an artery, the other 
into a vein, and we have then a patch or nodule of lymphatic tissue possessed of its 
own system of blood-vessels. By elongating and fusing they (patches or nodules) form 
a longer or shorter cord. As has been mentioned in a previous chapter, generally one 
or occasionally both surfaces of these lymphatic structures are covered, not with the 
ordinary flat large endothelial cells, but with germinating cells. 

In many instances these lymphatic structures have a long duration; they contain 
lymph-corpuscles, which are most probably produced in these structures by the connec- 
tive-tissue corpuscles ; we have then these structures acting like lymphatic glands. In 
other instances we find them only of a transitory character, being destined to change 
into fat-cell tissue ; they then become deprived of their lymph-corpuscles, and the con- 
nective-tissue cells, forming the bulk of the nodule, patch or cord, are transformed into 
fat-cells. We have then here a tissue possessed of its special system of blood-vessels 
and at one time functioning as lymphatic tissue, at another as fat-cell tissue. In some 
animals (guinea-pig, rabbit) and man a great part of the tissue in question remains 
lymphatic tissue, except under very favourable conditions of alimentation, when it is 
transformed into fat-tissue ; in others (carnivorous animals, mouse, rat) it is more 
readily changed into fat-tissue. 

Besides these there are small masses (small groups) of fat-cells found in some places of the 
serous membranes, which (fat-cells) are embedded in ordinary fibrous connective tissue and are 
derived from ordinary connective-tissue cells. 

In some connective tissues, as in the gelatinous tissue, mentioned in the preceding 
chapter, in the infraorbital fossa of rabbit and in loose cellular tissue, we find a similar 
condition, viz. vascularised groups of multiplying connective-tissue corpuscles preceding 
the appearance of fat in those cells. 

In all instances the transformation of a protoplasmic connective-tissue corpuscle 



n 



ATLAS OF HISTOLOGY. 

r t re l, takes place in this way : there appear, in the protoplasmic substance of 
,„to a fat-cell takes place f IobuleS] which increasing in number soon 

the connective-fssue ^^^ ^ bulk of the cell bec omes hereby, 

become confluent m one ,J ™^* ^ ^ ^ ^ one or tw0 large 

tr; itubstanL. in the ri P e state the fat-cell contains one lar g e fat^rop 

stlded by a thin mantle of original protoplasm, in one place of which the oblong 

U s is to be seen. Thus the fat-eel. may be described as a ves.de, whose wal „ the 

rig inal cell-protoplasm containing the nucleus, and whose contents . one large fa^drop. 

g D urin, starvation the fat-globule of the fat-cell disappears, and its place ,s taken by 

a clear serous fluid. In waste also this fluid disappears, and the fat-cell returns to the 

state of a solid protoplasmic corpuscle whence it started. 

In some instances fat-cells are formed also in other than the fixed connectwe-t.ssue 
corpuscles, viz. in the cells, which were mentioned in a former chapter as plasma-cells 
(W aldeyer), being larger than ordinary amoeboid connective-tissue corpuscles, pos- 
sessed of a single relatively large nucleus, and showing only slight ameebo.d movement. 
They contain occasionally coarse granules staining deeply blue m haematoxyhn ; 
these granules are converted into fat-globules, which gradually become confluent, and 
we have then a fat-cell that does not differ from the fat-cell above desenbed. Th s 
is, however, not the typical mode after which fat-cell tissue is produced, but only 
an incidental formation of fat in plasma-cells, especially to be observed under 
favourable conditions of alimentation. In the omentum of mouse and rat .solated 
plasma-cells may be noticed to undergo this change ; also in the mesentery m the 
subcutaneous tissue, in the connective tissue surrounding large vessels and nerve 
trunks, occasionally also in the intermuscular tissue of the tongue and other organs, 
the same change may be noticed. 



45 



CHAPTER VII. 

PIGMENT-CELLS. 

Pigment-cells proper (Chromatophores) are nucleated and branched connective-tissue 
corpuscles, the substance of which is filled, more or less uniformly, with pigment- 
granules. Their distribution is greater in the lower than in the higher vertebrates, and 
varies in different organs ; thus, for instance, the skin of lower vertebrates (fishes and 
amphibia) is by far the richest in pigment-cells, the internal connective tissues possess 
also a certain amount of pigment-cells, and the eye is supplied with pigment- 
cells in all vertebrates except albinos. The pigment-cells in the skin of lower 
vertebrates are as a rule flattened and larger than ordinary not-pigmented connective- 
tissue corpuscles ; their pigment varies not only in its colour — being under the microscope 
black, yellowish, bluish, greenish, or grey — but also in the shape of its particles, these 
varying from very minute spherical or angular granules to large elliptical or irregularly 
shaped plates and clumps. The amount and distribution of pigment in a cell 
determines the deeper or lighter shade of its colour. 

In the skin of lower vertebrates the pigment-cells in the state of rest are exceedingly 
richly branched cells, each with a nucleus, their dark (pigmented) branches anasto- 
mosing with each other and with those of their neighbours. The cell-substance seems, 
in some instances, to be almost entirely distributed in the pigmented processes, 
that is to say, there is not a conspicuous mass of pigmented matter as cell-body to be 
noticed around the nucleus. 

The same holds good for the serous membranes of lower vertebrates where the net- 
work of pigmented cells forms more or less continuous sheaths around arteries and veins. 
In the tissue of the iris and chorioides, and in the suprachorioides of man, and especially of 
dark-eyed mammals (sheep, ox), the pigment-cells are flattened nucleated cells, in which 
a relatively large cell-body surrounding the nucleus gives off numerous filamentous or 
platelike processes anastomosing with each other and with those of neighbouring cells. 

Pigment-cells alter their shape ; they are contractile under various influences, being 
capable of gradually withdrawing their pigmented processes : first they change from 
richly branched cells into cells with fewer processes, then the number of processes becomes 
smaller and these at the same time less branched, and finally all the pigment is 
retracted into an oval or slightly angular or spherical mass. This change has been 

H 2 



4 6 ATLAS OF HISTOLOGY. 

shown, at any rate for the cutaneous pigment-cells, to take place under the influence of 

chemical, mechanical and electrical irritation ; it is under the control of the nerves (Lister), 

and is influenced, as a reflex action, through the retina (Pouchet). The variation in the 

contraction of the pigment-cells of the skin in fishes and amphibian animals determines 

the change of colour observed in these animals (Leydig, v. Wittich, Briicke, v. Siebold, 

and others). The distribution of the pigment in a pigment-cell does not indicate the 

whole outline of the cell, and also the retraction of the pigment towards the centre, i.e. 

towards the nucleus, is not equivalent to a retraction of the cell-processes (Klein), 

inasmuch as only part of the cell-substance is retracted. It has been shown (Klein) 

that the substance of the pigment-cells when deprived of the pigment possesses a 

fibrillar structure, and interpreting this by the light of the experience on the structure of 

ordinary connective-tissue corpuscles — see Chapter IV. p. 29 — it is probable that the 

contractile part of a pigment-cell, viz. that containing the pigment matter, is only the 

fibrillar substance, intracellular network of fibrils, as distinct from the groundplate. It 

thus becomes intelligible that the extent of the pigment does not indicate the outline 

of the cell, nor do all parts of the cell contract while the pigment is being retracted 

towards the nucleus. 

Pigment granules are found, in the adult, in other organs than branched connective-tissue cells, 
as in the substance of hairs, in the deeper cells of the rete Malpighii of the epidermis, and in 
those of the epithelium of the mucous membrane of mouth of some mammals, in the endothelium 
lining the posterior surface of the iris and processus ciliares, in the epithelium lining the external 
surface of the retina, &c. In the superficial parts of the true skin in man and some mammals there 
are to be met with migratory connective-tissue cells containing a smaller or greater amount of 
dark brown pigment granules : it is highly probable that these migrants carry it to the rete Malpighii 
of the epidermis ; also in the skin of lower vertebrates (batrachian animals) migratory pigment- 
cells have been observed. 

PLATE X. 

Fig. I. drawn under a magnifying power of about 90; fig. III., under one of 
about 30; figs. II. IV. and V., about 350. 

Fig. I. From the omentum of cat, the blood-vessels of which had been injected 
with carmine-gelatin ; it shows (a) minute artery, (v) minute vein ; these two vessels 
are embedded in a cord of fat-cells (6) richly supplied with a network of capillary blood- 
vessels. The fat-cells are not represented as such, but their size may be recognised in 
most places, the meshes of the network of capillary blood-vessels not being larger than 
a fat-cell. 

(c) Lymphatic nodules ; only the nuclei of their cells are represented ; they are richly 
supplied with capillary blood-vessels from the same artery and vein as the cord of fat- 
cells. These lymphatic nodules are here the precursor of fat-tissue. 



■ HISTOLOGY. . 




PI X 







*Q 





i Nobie iittathieL 




Mmttrn Hio» xmf 



ADIPOSE TISSUE. 47 

Fig. III. From the omentum of guinea-pig, whose blood-vessels had been injected 
with carmine-gelatin : (a) artery, (z>) vein, (6) cord-like and nodular masses of cells, 
richly supplied with capillary blood-vessels. There is no fat formed yet in these lym- 
phatic nodules and cords. In the young examples of these (c) blood-vessels have not 
developed yet. 

Fig. II. From the omentum of young guinea-pig : 

(a) Minute artery. 

(v) Minute vein. 

(c) Capillary blood-vessels in the course of formation : they are not hollowed out 
yet completely, there being still left in them protoplasmic septa. As will be minutely 
described in the chapter on blood-vessels, the capillaries develope from nucleated cells, 
which become hollowed out ; this process consists in the vacuolation of cells, each of 
these possessing one, two, or three vacuoles finally becoming confluent ; gradually 
increasing they are brought in contact and ultimately fuse at their ends ; or one cell 
grows out into a nucleated solid protoplasmic filament or cylinder, in which vacuoles 
appear ; these increase in size and number, and ultimately fuse into one. The at first 
solid protoplasmic cylinder is thus transformed into a tube, the protoplasmic remains 
separating the vacuoles having all disappeared. 

(d) The ground-substance contains numerous nucleated cells, some of them are 
more distinctly branched and more flattened than others, appear, therefore, more spindle- 
shaped. These cells become converted into fat-cells, their interior becoming filled with 
one, two, or more fat-globules and their nucleus being pressed to the periphery ; 
so that in a fully-formed fat-cell we find one large fat-drop occupying the centre of 
the cell, and the original protoplasm, containing the nucleus, forming a mantle or cover 
round it. 

Fig. IV. Flat pigmented branched connective-tissue cells, pigment-cells, from 
the sheath of a large blood-vessel of mesentery of frog. The pigment is not distributed 
uniformly throughout the cell-substance ; being in some places collected in denser 
masses than in others, some parts of the cell look more black than others. Uncontracted 
state. 

Fig. V. Pigment-cells of a similar preparation as the preceding figure, but the cells 
have withdrawn more or less their pigment into the cell-body ; so that they appear 
smaller, more black, and less branched ; somewhat contracted. 



4 8 ATLAS OF HISTOLOGY 



CHAPTER VIII. 

CARTILAGE. 

This represents another division of connective tissues. In cartilage, as in other con- 
nective tissues, the cells, cartilage cells, are to be distinguished from the ground- or 
intercellular substance. The former are oval or spherical, occasionally flattened and 
branched, nucleated cells ; the latter varies in different cartilages, being in some quite 
hyaline, in others fibrous, and in others reticular ; hence the division into hyaline, 
fibrous and reticular cartilage. 

All cartilage, except the free surface of articular cartilage, is covered with a thin 
vascular connective-tissue membrane, the perichondrium, composed of fibrous con- 
nective-tissue bundles, between groups of which we find the interfascicular lymph- 
spaces, and in these the flattened connective-tissue corpuscles mentioned on former 

occasions. 

A. Hyaline Cartilage. 

Hyaline cartilage has a very wide distribution in the adult body, being present in 
some nasal cartilages, parts of sternum, ribs, larynx, and trachea ; on the articulation 
surface of bone as articular cartilage, no matter whether this surface is part of a free 
articulation or not. 

In most hyaline cartilages the cells are spherical or oval protoplasmic structures 
containing generally one spherical nucleus The protoplasm of the cells contains numerous 
fibrils twisted and crossing each other so as to form a feltwork (Schleicher, Flemming). 
In embryonal cartilage (very probably also in growing cartilage of adult) this fibrillar 
protoplasm is contractile (Schleicher). Occasionally smaller fat-globules are present in 
the cell-protoplasm. The nucleus contains within its limiting membrane a more or 
less well-defined network (Flemming). 

Each cartilage cell is placed in a cavity, lacuna, enclosed by a greater or smaller 
amount of hyaline ground-substance, a firm structureless substance yielding chondrin. 
The hyaline ground-substance around each cell represents a more or less polyhedral mass 
derived from the cartilage cell itself ; so that we may consider a given section of hyaline 
cartilage as composed of an aggregate of blocks, more or less polyhedral in shape, 
being pressed against one another, each of which consists of a hyaline matrix and a 
cartilage cell placed in its centre. 



HYALINE CARTILAGE 

49 

«r e "' inE h """' •"*" '" «* '"« ««™ - «** bio* become occa„o,„ ly 
demonstrated. S °' " bs) b '"" Ilci of "Cccdingly mtatt fibrik ^ ^ 

Hyaline cartimges differ among,, each other in the distribution of the hyaline 
^"7 aro 7 d "" * Ei "» *• ««"re surrounded b y almo, 
s.ed masses of grouod-substance as in h y a,i„e cartilage of trachea and ,ar y „/„T 



nan 
is 



ess regular, a s i„ some articular ear,i Ia ges, beiog present aroand the oells in some parts 
a larger amount thau ,„ others. Again, in some parts of o„. and ,,« same calge 



abundant than in others; eomparing. for instance,*, parts near the X" Z 
surface of a cartilage with the deeper parts, tee notice ,h„ the eells lie much close, 

together in the former than in the latter. 

When the cells are so closely placed together that hardly any, or at any rate no 
consp.cuous amount of, hyaline ground-substance is to be noticed, the cartilage is called 
parenchymatous cartilage; embryonal cartilage at an early stage, the marginal parts 
of some adult cartilages, and certain other cartilages are of this nature 

In the fresh and living state the cartilage cells are filling up almost entirely their 
respective lacunae, but after death, and especially after reagents, they shrink away from 
then- wall m a greater or lesser degree, and are converted into irregular-shaped, angular 
or even star-shaped masses. Under these circumstances a delicate homogeneous limiting 
membrane becomes visible, forming the boundary between the lacuna and the hyaline 
ground-substance. In growing cartilage this limiting membrane becomes gradually 
th.ckened and represents a special layer of hyaline substance formed from the periphery 
of the cell-substance. In such cartilage we therefore distinguish two different parts 
of the hyaline ground-substance, viz. one portion that is the general matrix, and 
another that forms a thinner or thicker capsule directly around the cartilage cells 
(Kolhker). The former is older than the latter, this being more recently formed. 

In growing cartilage the cells undergo division : the cell that is to divide enlarges 
its nucleus divides— cartilage cells with two nuclei ; then the cell-substance divides, and 
thus two daughter-cells are formed. 

In some cartilages the two daughter-cells very soon give origin to a new genera- 
tion, thus forming a group of four cells; or to two generations successively, thus forming 
a group of eight cells ; in others the first two daughter-cells, before again dividing, become 
separated by a considerable amount of hyaline matrix derived from them. 



50 ATLAS OF HISTOLOGY, 

The irregular distribution of hyaline ground-substance around the cartilage-cells, mentioned 
above, is in a great measure due to some cartilage-cells, or groups of them, undergoing a more 
rapid increase in number, and hence are surrounded by less hyaline ground-substance than 
others. 

It is doubtful whether in the process of reproduction the division of the cell-sub- 
stance is always caused by a septum in conjunction with the capsule, and therefore it is 
also doubtful whether the daughter-cells are primarily disconnected from each other, being 
enclosed in their separate lacuna (Leidy, Claparede, Heidenhain, and especially Schleicher), 
seeing that in many instances the first two daughter-cells, and even a group of cartilage 
cells, may be seen aggregated within a common lacuna. 

The ground-substance of hyaline cartilage is not altogether solid, but contains 
numerous fine channels permeating it (Bubnoff) ; these channels form the anastomosing 
canals between neighbouring lacunar (Heitzmann, A. Budge). Arnold has shown that 
the capsule of each cartilage cell is permeated by numerous very fine radiating canals. 
Thus the hyaline cartilage possesses, just like fibrous-connective tissue, an anastomosing 
system of lacunae and canals (A. Budge, Arnold, Nykamp), which will be mentioned in 
the chapter on the Lymphatics as forming the lymph-canal system of the hyaline car- 
tilage in connection with the lymphatics of the perichondrium. Near the perichondrium 
the cartilage cells become flattened and smaller than those of the depth, and in some 
localities, e.g. near the surface of articular cartilage and near the junction of this and the 
synovial membrane, are even branched (Hiiter, Albert, Rayner), and in the latter place 
form a direct connection with the branched connective-tissue corpuscles. 

A peculiar arrangement of cartilage-cells — viz. in more or less paralled rows — 
exists in the hyaline cartilage that unites the diaphysis with the epiphysis of long bones. 
This is called ossifying or, better, intermediary cartilage, and will be more particularly 
noticed, in connection with the growth of bone, in the next chapter. 

The ground-substance of hyaline cartilage becomes occasionally, especially in the 
process of development of bone in cartilage, in advancing age, or under pathological 
conditions, the seat of a deposit of lime matter, calcification of cartilage, in the form of 
opaque roundish angular or irregularly shaped masses. The deposit of lime matter 
commences next to the cartilage cell (Ranvier). 

No nerves or blood-vessels have been seen in hyaline cartilage except those of its 
perichondrium. 

B. Fibrous Cartilage. 

This form of cartilage is also called white fibrous- or connective-tissue cartilage. 
It occurs as cartilagines interarticulares, ligamenta intervertebralia, cartilago symphysis 



FIBROUS CARTILAGE. $1 

pubis, sesamoid cartilages, the cartilages forming the margin of a fossa glenoidalis & c 
In all these instances the ground-substance is composed of bundles of ordinary fibrous 
tissue, forming occasionally more or less distinct lamellae, which in a few instances (ligam 
intervertebr. and cartilage symphysis pubis) possess a concentric arrangement. On the 
surface of the bundles, or rather of groups of bundles, are placed, similarly as in tendon or 
fasciae, rows of slightly flattened elastic cells (Boll), each with a round nucleus and 
enclosed in a distinct capsule. As a general rule, where this form of cartilage is present 
in large and continuous masses, there is no hyaline cartilage substance to be seen 
around the cells ; but when it is interspersed in tendinous tissue, as in the tendo 
Achillis, near the insertions of tendons on bone, besides the above form, also isolated 
cells or groups of them may be seen surrounded by a smaller or larger amount of hyaline 
matrix. 

When tendinous tissue passes into fibrous cartilage, as where tendinous tissue 
is fixed on the fibrous cartilage (Iigamenta intervertebralia) or in the cartilagines 
sesamoideae of tendons, the bundles of connective tissue of the tendon pass without 
interruption into those of the fibrous cartilage, and so do also the cells, retaining their 
arrangement in rows, and their relation to the surface of the group of bundles, but the 
cells, besides being less flattened at the point of transition into the fibrous cartilage, 
become invested, as mentioned above, in a thin capsule. 

At the point of transition of fibrous into hyaline cartilage, as at the margin of the 
Iigamenta intervertebralia, or the cartilago symphysis pubis, the fibrous matrix of the 
former passes insensibly into the hyaline substance of the latter, and the cells of the one 
into those of the other ; when entering the hyaline cartilage, the cells of course change 
their shape, losing their flattened character, and their arrangement is no longer in rows. 

C. Reticular Cartilage. 

This is also called yellow or elastic cartilage. It occurs in the ear-lobe, larynx 
(epiglottis, cartilagines Wrisbergi and Santorini, the cartilaginous nodule or rod occa- 
sionally found in the true vocal cord) and tuba Eustachii, Reticular cartilage in the 
adult state is hyaline cartilage permeated by elastic fibrils. These are arranged so 
as to form the trabecular of a reticular or spongy framework ; within the trabecular the 
elastic fibrils branch repeatedly, and anastomose with each other and cross one another 
in all directions. The meshes of the reticular framework contain the cartilage-cells 
singly or in groups, surrounded by a smaller or larger amount of hyaline cartilage 
substance. 

Different cartilages of this species vary in the relative amount of hyaline ground- 

i 



5 2 ATLAS OF HISTOLOGY. 

substance and elastic framework, and the same may be said of one and the same 
reticular cartilage in different states of development. They all commence as hyaline 
cartilage enclosed in perichondrium ; as development advances numbers of elastic fibres 
appear in the hyaline ground substance ; these branch and anastomose with one another. 
In a still further stage the networks of elastic fibres reach such an extent that they 
constitute a conspicuous part of the ground-substance, forming the network of trabecular, 
as described above. The hyaline cartilage-substance is now limited only to the meshes 
of the reticular framework containing the cartilage cells. 

In the cartilaginous nodule, present in some instances near the margin of the human true 
vocal cord, we find the elastic fibres not arranged so as to form a reticular framework of trabecular, 
but permeating the cartilage as a uniform network of fibrils. 

Examining sections through the epiglottis of children, we find the reticular framework of 
elastic fibres not reaching quite up to the superficial part, viz. that next the perichondrium, this 
(superficial part) being still almost entirely composed of hyaline substance. The cartilage is, in 
children, not a continuous plate, as usually represented, but in many instances consists of several 
isolated plates placed in a longitudinal series. As growth proceeds they become gradually con- 
fluent into a reticulate plate. In the epiglottis of some mammals (dog, cat, rabbit) a great portion of 
the reticular framework of elastic fibres does not contain hyaline cartilage in its meshes, but fat- 
cells singly or in small groups. 

As in ordinary hyaline cartilage, so also in reticular cartilage, we meet with a 
perichondrium composed of vascular fibrous connective tissue and with the flattened 
connective-tissue corpuscles in the interfascicular spaces. 

A communication, by means of broader or narrower canals, between the inter- 
fascicular spaces of the perichondrium and the lacunae of the cartilage cells, mentioned 
in ordinary hyaline cartilage, exists also in reticular cartilage. Here the lacunae of the 
cartilage cells anastomose with each other throughout the cartilage. 



PLATE XL 

Figs. I. and III. drawn under a magnifying power of about 350 ; fig. II., about 
90; figs. IV. and V., about 150; figs. VI. and VI 1 1., about 350; and fig. VI L, 
about 450. 

Fig. I. From a longitudinal section of tail of mouse; portion of intervertebral 
fibrous cartilage (connective-tissue cartilage) viewed from the surface. Bundles of 
fibrous-connective tissue in two layers crossing each other at a right angle ; between, or 
respectively on, the bundles are roundish or oblong cartilage cells, each with a clear 
nucleus ; the cells are each enclosed in a capsule, and are flattened when viewed in 
profile. 









■ .* 





- . 



i 



- 




. 



V] 



.. 



STRUCTURE OF CARTILAGE. 53 

Fig. II. Transverse section through the same intervertebral cartilage. This being 
composed of concentric lamellae (of fibrous tissue) arranged around a central cavity 
filled with gelatinous substance, shows in a transverse section parallel strata. The 
lower edge of the figure is the part next that central cavity, the lamellae are here less 
distinct, and this part becomes more deeply stained in logwood. Between the lamellae are 
the cartilage cells, arranged in rows. The cells are in this and the following figure III. 
represented as seen in profile; being flattened, they appear staff-shaped. As figure III. 
(higher magnifying power) proves, each cell lies in a capsule. A distinction between 
nucleus and cell-substance is not indicated in this drawing. 

Fig. IV. Ordinary hyaline cartilage of trachea of a child. The cartilage cells are 
enclosed singly or in pairs in a capsule of hyaline substance. The distinction between 
nucleus and cell-substance of the cartilage-cells is not brought out, owing to the low 
magnifying power under which the drawing was made. This capsule of hyaline 
substance is the most recently formed part of the cartilage matrix. The rest of the 
hyaline matrix shows a differentiation into a less stained substance in the vicinity of the 
cartilage cells and their capsules, and a more deeply tinted part, farther away from the 
cartilage cells. The cause of this is not easily ascertained. 

Fig. V. From a longitudinal section through tail of mouse, showing the transition 
of fibrous cartilage (a) into ordinary hyaline cartilage (6), and this again into inter- 
mediary cartilage (c) ; in this latter the cartilage-cells are arranged in vertical rows ; it 
corresponds to the intermediary cartilage placed between epiphysis and diaphysis of 
long bones (see chapter on Bone). The fibrous nature of the matrix of (a) is, on account 
of the low magnifying power, not shown. The cartilage cells of (6) and (c) are much 
shrunk. 

Fig. VII. From the same preparation as hg. IV., but under a higher power, 
representing a group of cartilage cells. Some of these cells possess one nucleus, others 
two. It is here seen that the capsule of hyaline substance is derived from the cell- 
substance, owing to a peculiar change of its periphery. 

Fig. VI. From a vertical section through the reticular (yellow or elastic) cartilage 
of epiglottis of a child. 

a. Perichondrium ; the connective-tissue bundles forming the matrix of this mem- 
brane are not represented, only the flattened (therefore in profile staff-shaped) nuclei of 
the connective-tissue corpuscles are shown here. 

b. The part of the elastic cartilage next the perichondrium. The matrix, composed 
of networks of minute fibrils, is arranged as a network of trabecular ; in the meshes 
lie cartilage-cells embedded in hyaline (stained) substance. The cell-substance of the 
cartilage-cells is not well shown here, and their nucleus is much shrunk. 



54 ATLAS OF HISTOLOGY. 

Fig. VIII. From a vertical section through the elastic cartilage of ear-lobe of pig. 
The explanation is here the same as in tig. VI. 

In both these instances, viz. figs. VI. and VIII., the cartilage-cells are embedded 
in hyaline substance ; it has been, however, omitted to represent the cells as situated in 
lacuna?, which anastomose with each other by finer or broader canals. The same 
communication exists also between the lacunae of the cartilage-cells and those of the 
cells of the perichondrium. In this latter place they are the interfascicular spaces, as 
has been figured in fig. IX. of Plate VIII., and mentioned on p. 32. 



55 



CHAPTER IX. 

BONE TISSUE. 

Bone or osseous tissue forms the third section of the group of connective tissues, 
fibrous tissue, including elastic tissue, being one, and cartilage the other section. 
Osseous tissue has, in the adult, a greater distribution than either of the other two, form- 
ing the whole skeleton and part of the teeth, the cement ; in lower vertebrates it is found, 
in addition, also in other parts, as skin, sclerotic membrane, &c. 

As in other connective tissues, so also in bone we distinguish the ground-substance, 
or matrix, from the cells, bone corpuscles, embedded in it. The matrix is a firm 
brittle substance uniformly impregnated with insoluble inorganic salts, chiefly lime salts 
(carbonate of lime, basic phosphate of lime, magnesia, &c.) ; it appears transparent when 
examined in a thin section under the microscope. By adding acids to it, the insoluble 
lime salts are converted into soluble ones, and the bone ground-substance is thus 
gradually freed of them. The organic basis of the ground-substance, the ossein, 
presents itself, under these conditions, as a dense mass of minute fibrils, arranged 
either parallel or interlacing each other in a complex manner or joined in a network. The 
arrangement of these fibrils into well-defined groups determines the lamellar nature of 
the ground- substance (v. Ebner). These fibrils comport themselves in chemical respects 
like fibrous connective tissue, swelling up by the action of acids, and yielding, when 
subjected to boiling, glutin or gelatin. 

The bone corpuscles are more or less elongated lacunae possessed of numerous fine 
branched and unbranched canals, by means of which neighbouring lacunae anastomose 
with one another. The processes pass in all directions, and are more or less wavy and 
twisted. Each lacuna with its canals contains a flattened nucleated protoplasmic cell, 
the bone cell proper, possessed of numerous fine processes. The relation between the 
bone lacuna and canals, on the one hand, and the bone cell and its processes, on the other 
hand, is precisely the same as that mentioned of the connective-tissue corpuscles of the 
cornea (see Plates VII. and VIII. p. 30), viz. the lacunae with their anastomosing canals 
form one intercommunicating system of spaces, the lymph-canal system, lined with the 
flattened nucleated branched and anastomosing bone cells. 

The osseous ground-substance possesses in most instances lamellar structure, the 
lamellae being then separated by rows of the oblong-bone corpuscles. The corpuscles 

K 



56 ATLAS OF HISTOLOGY. 

placed between two contiguous lamellae anastomose by fine transverse processes; 
owing to the great number of these processes the lamellae possess a fine transverse 
striation. In some bones, as in microscopically thin bone-plates, the ground-substance 
does not exactly present the lamelhr structure, showing an arrangement in band- 
like stripes ; the bone corpuscles are then distributed more or less regularly between 

these bands. 

There are two principal modes of arrangement of osseous tissue : (a) as compact, and 
(b) as spongy substance. The bone-matter surrounding the central or marrow cavity 
of the shaft of all long bones, and the outer crust of all short and flat bones, is compact 
substance ; whereas the spongy network of bone lamellae and bone trabecule, containing 
in its meshes vascular marrow, is present in the centre of the epiphysis and in the 
extremities of the diaphysis of long bones ; the diploe of short bones and that of flat 
or tabular bones is likewise made up of spongy bone-substance. 

A. In the compact bone-substance we distinguish the following parts : — i. Haversian 
canals : these are fine canals of various lengths pervading the compact substance in a 
longitudinal direction, and anastomosing with one another by more or less oblique or 
transverse branches ; they open not only into the central or marrow cavity (or cavities) 
of the bone, but also on the outer free surface. Near the marrow cavity the Haversian 
canals are larger than those next the outer surface. Each Haversian canal contains a 
blood-vessel, one or two lymphatics, and, according to its size, a greater or lesser amount 
of connective tissue, which is identical with that of the tissue of the marrow, to be 
described below. 2. Bone lamellae and the corresponding bone corpuscles between 
them. The bone corpuscles next to the Haversian canals, by their canaliculi, freely 
anastomose with the lymphatics of the latter (A. Budge). 

The lamellae possess in the compact substance of human bones the following typical 
arrangement : — 

a) Concentric or Haversian lamellae directly surrounding the Haversian canals. 
Each of these canals possesses its own system of such concentric lamellae. Their numbers 
vary in different parts, from four to fifteen being found in one system. The number of 
lamellae is always smaller near the external surface of the bone than in its deeper 
parts. 

The fine radiating striation of these concentric lamellae is owing, as has been ex- 
plained above, to the numerous fine canaliculi passing between the neighbouring bone 
corpuscles. 

b) The interstitial or ground lamellae. The lamellae interposed between the Haver- 
sian systems of concentric lamellae form also groups running in various directions more 
or less curved : they are the interstitial or ground lamellae. The size of these groups 



ARRANGEMENT OF BONE LAMELLAE. 57 

depends of course on the closeness of the position of the Haversian systems, being very 
small when these latter are in almost immediate contact, and larger when they are 
further apart. 

c) Those groups among the interstitial lamella? which possess a direction parallel to 
the surface of the bone are designated under the special name of the circumferential 
lamella?. They are best seen near the external free surface of adult lone bones 
(Tomes and de Morgan). 

Not only in the compact substance of long bones, but also in that of short and flat 
bones, we find the above arrangement of the bone lamellae, provided the thickness of 
the bone is sufficiently great to permit of it ; but when, as in some instances of short 
and flat bones, the compact substance forms only a thin cortex, the bone lamellae 
are reduced to groups that run parallel to the surface. 

B. In spongy bone the lamellae are arranged as larger or smaller groups, branching 
and anastomosing so as to form a network of broader or smaller plates and trabecular ; 
the meshes of this network, viz. the marrow cavities, intercommunicate with each other, 
and are filled with a very vascular connective tissue of a peculiar structure, to be de- 
scribed below as red marrow. The bone corpuscles between the lamellae of the above 
plates and trabecular anastomose by means of their canaliculi with the marrow cavities. 

Spongy bone-substance varies in different parts, according to the manner of ar- 
rangement of its plates and trabecular ; thus, in the extremities of the shaft of long 
bones the meshes are pre-eminently oblong in a longitudinal direction, and hence the 
spongy substance when viewed with the unaided eye or a lens appears longitudinally 
striated. 

The lamellae of compact substance are perforated by more or less perpendicular fibres, 
the perforating fibres of Sharpey. They are fibrous bundles, and run either singly 
or in groups, and, just like the lamellae, are impregnated with lime salts. As will be 
described below, they are present in all bone developed in connection with the perios- 
teum, and they themselves owe their origin to this latter, hence the perforating fibres 
in the adult are still connected with the periosteum (Kolliker). Some of the per- 
forating fibres are very fine, and of the nature of elastic tissue (H. Muller, Schafer). 

Besides the branched cells situated in the lacunae and canaliculi of the ground- 
substance, and the vessels mentioned in the Haversian canals, there are two other soft 
tissues to be considered in connection with bone, viz. the periosteum and the marrow. 

The periosteum is the layer of tissue covering the free surface of a long, short, or flat 
bone. It consists in all instances of (a) an external dense, and (6) an internal loose layer. 

a) The external layer is a dense fibrous tissue, hence it is called the fibrous 
layer. In some bones it is thin, and composed of a single layer of bundles of 



K 2 



5 g ATLAS OF HISTOLOGY. 

fibrous tissue ; in others the bundles are arranged in two or more layers. Between 
the o-roups of bundles, viz. in the interfascicular spaces, we meet with the ordinary flat- 
tened connective-tissue corpuscles. A limited number of capillary blood-vessels sup- 
ply this fibrous layer. 6) The internal layer, or osteogenetic layer, contains a plexus 
of more or less slender bundles of connective-tissue fibrils ; embedded in it are numerous 
capillary blood-vessels and a great many cells, each of which possesses a round or 
oval nucleus. The cells vary in shape, being either spherical, oval, spindle-shaped, or 
branched. They occupy the meshes between the fibre-bundles. In some places the 
plexus of these is very regular, and their meshes are completely filled with the cells. 
In growing bone we find a network of (young) bone lamellae, terminating in the 
shape of pointed trabecular within the osteogenetic layer of the periosteum ; these 
young bone lamellae are in many places covered with an epitheloid layer of those 
cells, called osteoblasts (Gegenbaur). The osteoblasts are concerned in the formation 
of these young bone lamellae, as will be described minutely below. 

The marrow contained in the cavities of bone is of a twofold nature, yellow and 
red. Both possess a rich supply of blood-vessels (arteries, veins, and capillaries), of 
which even the largest branches are notable for their exceedingly thin wall. The 
yellow marrow filling the central cavity of long bones is chiefly composed of fat cells, 
and hence its yellow appearance ; between these are membranes of flattened connective- 
tissue cells, and various numbers of polyhedral, spherical, or oval cells, each with one 
or two nuclei. These latter represent the marrow-cells proper; they resemble lymph 
corpuscles as regards size and aspect. Red marrow is the vascular substance filling the 
meshes of spongy bone ; it contains only few fat cells, and is chiefly made up of marrow 
cells. Amongst these there are in many localities, as in ribs, bodies of vertebrae, ex- 
tremities of diaphysis of long bones, peculiar cells, each of which is slightly larger than 
a coloured blood-corpuscle, and whose substance is of a uniform yellowish-green tint, 
like that of a coloured blood-corpuscle. They contain, in addition, a nucleus. They 
are supposed to be transitional forms between marrow-cells and coloured blood- 
corpuscles (Neumann, Bizzozero). 

If this be the case, the marrow of spongy bone has the important function of the 
formation of coloured blood-corpuscles. That the marrow of bones, especially the red 
marrow, has an intimate relation to the lymphatic glands is made probable by the fact 
that the former is found frequently diseased with the latter. 

Conspicuous amongst the marrow cells, especially in red marrow, are the multinu- 
clear giant cells (myeloplaxes, Robin) ; their function and their relation to bone and 
cartilage will be mentioned below in connection with the development of bone. All 
these cells show amoeboid movement when examined under suitable conditions. 



JUNCTION OF CARTILAGE AND BONE. 59 

Where spongy bone is in immediate contact with hyaline cartilage, as is the case in 
the apophyses and extremity of the shaft of long bones, in some parts of short and flat 
bones there exists a peculiar relation between the two tissues. Passino- from the 

o 

hyaline cartilage into the spongy bone the following layers may be distinguished :— 

1) After passing the ordinary hyaline cartilage we enter into a broader or narrower 
layer of hyaline cartilage, in which the lacunae for the cartilage cells are greatly enlarged, 
and hence the hyaline ground-substance is much reduced in amount ; the cartilage cells 
themselves are very transparent, and their nucleus much swollen ; in many instances 
their disintegration has commenced. This layer of ' large cartilage lacunar * is for 
obvious reasons more transparent than the other hyaline cartilage, and hence is 
easily recognised even on inspection with the unaided eye. 

2) In the next layer the lacunae of the cartilage cells become more or less confluent, 
and the cells themselves are seen gradually to break down into irregular amorphous 
matter, the hyaline ground-substance of the cartilage becoming at the same time 
impregnated with lime-salts, i.e. calcified. This and part of the following layer repre- 
sent what is sometimes called the zone of ossifying cartilage ; but as the cartilage does 
not ossify — that is to say, is not converted into bone, but is merely calcified — it should 
be more appropriately called zone of calcified cartilage. 

3) In this layer the lacunae of the previous zone are large intercommunicating cavities 
filled with marrow, chiefly capillary blood-vessels and marrow-cells. The blood-vessels 
form loops, and do not pass into the previous layer. 

The spongy network of hyaline ground-substance separating the cavities — marrow- 
cavities — is also here calcified. 

We speak of the parts of the framework of this and other spongy matter as ' trabecular' 

The marrow cells next the trabecular of calcified cartilage arrange themselves so as to 
form a more or less continuous epitheloid covering, osteoblasts, the individual cells 
being either oblong, or spherical, or branched ; they are slightly larger than the other 
cells of the marrow cavities. Amongst the osteoblasts are multinuclear giant cells. 

Passing on towards the depth, there appear thinner or thicker lamince of osseous 
substance on the surface of the calcified cartilage trabecule ; and the further we pass the 
more continuous do these osseous laminae become — that is to say, the more perfectly do 
the calcified cartilage trabecule become covered with osseous substance (bone matrix and 
bone corpuscles) ; the calcified cartilage diminishes in amount as a greater depth is 
reached. 

4) Finally, we arrive at a spongy substance that possesses all the characters of spongy 
bone, but differs from this in so far as its trabecular are not so thick, and as they include, 



6o ATLAS OF HISTOLOGY. 

from place to place, in their centre a thinner or thicker, longer or shorter, remnant of 
unabsorbed calcified cartilage. The surfaces of the now osseous trabecular are covered 
with osteoblasts, among which multinuclear giant cells are still to be met with. 

The different layers described in the preceding are not sharply defined from, but 
gradually merge into one another. Their thickness and distinction vary in different 
bones ; it is best marked in long bones, where the articular cartilage joins the spongy 
bone of the epiphysis, and at the point of contact of the intermediary cartilage and the 
spongy bone of the extremity of the diaphysis. In the latter instance the character of 
the layers is one of a distinctly longitudinal design, owing to the peculiar nature of the 
intermediary cartilage. 

This cartilage contains longitudinal rows of cartilage cells. The individual cells are 
more or less distinctly flattened in a transverse direction. Near the distal end, that is 
the end further away from the diaphysis, the cartilage cells are more flattened and more 
closely placed within the same row than at the proximal end ; they are at the same time 
conical, and so placed within the row that with their thinner part— the wedge of the 
cone— they are, as it were, pushed over one another (Aeby). This appearance is due 
to each cell dividing in a diagonal. Approaching the proximal end, the cartilage cells 
become laro-er in a vertical diameter, and the individual rows become further apart from 
each other ; the result is that the amount of hyaline ground-substance separating the 
individual cells within a row is reduced, while that between the rows increases. 

The layers which now follow up to the spongy bone are the same as those described 
above, but possess, for obvious reasons, a pre-eminently longitudinal design, as explained 
above. 

To repeat, they are : first, the transparent layer or the layer of large cartilage 
lacuna, then the zone of calcified cartilage, further the layer containing already vascular 
marrow in the cavities, and osteoblasts on the surface of the calcified cartilage trabecular, 
then the layer in which, in addition, the calcified trabecular become ensheathed with 
laminar of osseous tissue, and finally true spongy bone, the calcified cartilage having 
altogether disappeared (by absorption). 

The description given here of the nature of the junction of hyaline cartilage and 
spongy bone indicates at the same time the manner in which the development of bone 
in cartilage, and the growth in length of the spongy bone of the diaphysis, i.e. its encroach- 
ment on the intermediary cartilage, take place ; it is only necessary to remember that it 
is the vascular marrow, with its osteoblasts, which gradually grows into the cartilage, 
and at the line of contact produces in it the definite changes which receive their 
expression in the above layers. 

All bones, except the tegmental bones of the cranium, and the greater part of the 



DEVELOPMENT OF BONE. 61 

facial bones, are at an early stage of embryonal life preceded by solid hyaline cartilage. 
This does not ossify at any time, and does not therefore become converted into the 
bone tissue, but is replaced by bone formed directly or indirectly from the perios- 
teum. Sharpey, E. H. Weber, Loven, and others first taught this doctrine ; the 
researches of H. Miiller, Gegenbaur, Landois and Waldeyer fully established it. The 
same mode of development, viz. from the periosteum, exists also in the case of the 
tegmental bones of the skull and those of the face, and there is no essential 
difference in the development of bone in cartilage, intracartilaginous or endochon- 
dral (Strelzoff) bone, and in bone that is formed without the intervention of cartilage in 
membrane, intermembranous or periostal bone. 

Endochondral Bone. 

\st Stage. Solid hyaline cartilage covered by perichondrium; this latter is identi- 
cal with the periosteum whose place it holds in this and the subsequent stage. It con- 
sists, like the periosteum, of an external and internal layer ; owing to the early stage 
neither of these two layers possesses any fibrous tissue yet, but instead of it, spindle- 
shaped embryonal cells, similar to other connective tissues in the foetal state. But 
there is a definite distinction between the two layers, the internal or osteogenetic layer 
containing numerous spherical cells (the future osteoblasts), and many blood vessels, 
whereas the outer layer has the uniform structure of embryonal connective tissue. 

2nd Stage. The osteogenetic layer of the perichondrium penetrates, in the shape 
of longer or shorter processes (periostal processes, Virchow), into channels of the 
cartilage formed for them, and probably by them, through absorption. Thus the 
cartilage becomes gradually permeated by a system of anastomosing channels, cartilage- 
channels, containing a vascular tissue, rich in cells, and derived from the osteogenetic 
layer of the perichondrium. This change may be appropriately called that of 
Chondroporosis, and it starts at the so-called points of ossification. 

3rd Stage. The cartilage around the oldest cartilage-channels becomes more transpa- 
rent owing to the lacunas of the cartilage cells becoming larger and the cells themselves 
more transparent. Then the lacunae next the channel become confluent with this latter, 
the corresponding cartilage cells having been disintegrated, and the trabecule of ground- 
substance separating the lacunae having undergone calcification. Instead of the single 
cartilage-channels with smooth outline of the former stage, we now find in these places 
irregular cavities, into which projects a network of trabecular of calcified cartilage. These 
irregular cavities, primary marrow cavities, are filled with the tissue that was originally 
contained in the cartilage-channels, viz. the periostal processes derived from the 
osteogenetic layer of the periosteum, the tissue in question having, of course, undergone 



62 ATLAS OF HISTOLOGY. 

great increase. This tissue, which, as stated above, contains numerous vessels and cells, 
is now, viz. when filling the primary marrow cavities, called primary marrow. The reader 
has no doubt become already aware, that the primary marrow cavities, the primary 
marrow, the surrounding calcified cartilage and the adjoining zone of large and transpa- 
rent cartilage cells, are in every respect analogous to the structures present at the point 
of junction of spongy bone and hyaline cartilage in the growing and adult bone, as 
described on a former page. And just as in the case of the growing and adult bone, so 
also in the first development of endochondral bone, the cells of the marrow arrange 
themselves (by active multiplication) as an epitheloid layer, osteoblasts, on the sur- 
face of the calcified cartilage trabecule, and these become gradually ensheathed in true 
osseous tissue produced by those osteoblasts. 

4 t/i Stage. The number of primary marrow cavities, filled with marrow, increases, and 
the trabecule of calcified cartilage, having become ensheathed with a considerable layer 
of osseous tissue, are gradually absorbed. We have now, instead of a network of 
calcified cartilage trabecule, as in the previous stage, a network of osseous trabecular, 
including in their interior remains of the unabsorbed calcified cartilage. These remains 
are gradually reduced to longer or shorter angular masses, and finally disappear alto- 
gether, so that the trabecular are now altogether composed of osseous substance. We 
have then the condition of embryonal spongy bone. The further away from the ' point 
of ossification 'the younger and the thinner are the trabecule, and the more of the 
remains of unabsorbed calcified cartilage do they contain. 

The nearer to the ' point of ossification,' the place whence the process originated, 
the thicker do we find the trabecule, and the more does the tissue as a whole resemble 

spongy bone. 

The surface of the osseous trabecular is in all parts covered with osteoblasts, and the 
cavities separated by the trabecular are filled with marrow, rich in vessels and cells. 

In the embryonal spongy bone the osseous matrix does not possess lamellar struc- 
ture, but forms a peculiar trellis-work (v. Ebner). 

S th Stage. The next stage is the absorption of the endochondral spongy bone, begin- 
ning in the centre, and gradually extending towards the periphery, the trabecular becoming 
thinner, and finally altogether disappearing ; the meshes of the spongy bone become 
hereby confluent into one large cavity, the central marrow cavity, filled with marrow. 

Simultaneously with this, another very important change takes place, viz. the develop- 
ment of bone from the periosteum around the endochondral bone. The osteoblasts 
of the osteogenetic layer of the periosteum form (by multiplication) longer or shorter 
anastomosing rows of cells, which give origin, in the manner described above, to a network 
of trabecular of osseous substance. New layers of osteoblasts (derived from the cells of 



PERIOSTAL BONE. 6 3 

the osteogenic layer) appear on the surface of these trabecule, and by undergoing the 
same change, viz. into osseous matrix and corpuscles, the trabecule increase in 
thickness. 

The formation of new osseous tissue extends gradually in breadth and depth, and 
we thus obtain in connection with the osteogenetic layer of the periosteum a stratum of 
spongy periostal bone around the previously formed endochondral bone. The 
trabecular are covered with osteoblasts ready to be converted into osseous substance. 
This is especially well shown in the immediate neighbourhood of the osteogenetic layer, 
where the youngest trabecule are found ; these generally originate, as pointed masses, 
in connection with isolated and bundles of fibres of the periosteum. The continuity 
of the fibres of the periosteum with the youngest layer of bone trabecular persists, and 
represents the rudiments of the perforating fibres of Sharpey. The amount of 
the periostal bone is in an inverse ratio to that of the endochondral bone. In the 
shaft of long bones we find, for instance, the periostal bone of great thickness in the 
centre, at a time when at the extremities only the first trace of it makes its appearance. 
Again, at a time when the endochondral bone in the former locality has been already 
almost entirely absorbed into the central marrow cavity, in the latter place, viz. the 
extremities of the shaft, it is as yet only in the third or fourth stage. 

The meshes of the spongy periostal bone are the so-called Haversian spaces, and 
contain marrow, which is merely a continuation of the tissue of the osteogenetic layer 
of the periosteum. 

6th Stage. In this stage all or nearly all endochondral bone is absorbed, and the 
spongy bone constituting the shaft is all derived from the periosteum. But also a 
certain amount of the trabecular of this bone becomes absorbed, whereby the meshes of 
the spongy bone become enlarged (Osteoporosis, Schwalbe). 

After this a system of concentric lamellar is formed in each Haversian space by 
its marrow. The spaces are hereby gradually reduced to the Haversian canals, and the 
spongy bone is thus transformed into compact substance. 

The remains of the original trabecular of the spongy (periostal) bone represent the 
interstitial or ground-lamellar separating the systems of concentric (Haversian) lamellar. 
The process of osteoporosis and the formation of concentric lamellae comprises only 
the deeper and middle portions, it does not involve the superficial or youngest layer. 

At birth the original endochondral bone has already entirely disappeared in many 
bones, and the compact and spongy substance present are derived from the periosteum, 
except the spongy bone in the apophyses and in the extremities of the diaphysis, this 
being endochondral bone. As the formation of bone by the osteogenetic layer of the 
periosteum continues, the oldest parts, viz. those first formed, and situated near the 

L 



64 ATLAS OF HISTOLOGY. 

central marrow cavity, become absorbed : after birth we find that in this way even 

portions of the original periostal bone have already been absorbed in the central cavity. 

The primary formation of spongy bone by the osteogenic layer of the periosteum, 
and the conversion of it into compact bone, as described above, represents at the same 
time the manner, in which all bones increase in thickness during foetal life as well as 
after birth, as long as they continue to grow. When new bone is formed under abnormal 
conditions, as in plastic operations, osseous tumours, &c„ it is eminently the osteo- 
genetic layer of the periosteum which produces the new bone-substance. The growth 
in length of the diaphysis of long bones has been described before as an encroachment 
of the spongy bone of the extremity of the diaphysis on the intermediary cartilage. 



In this and in all other instances ol the formation of osseous substance, the osteo- 
blasts are the elements which produce both the osseous matrix and the bone corpuscles 
(Gegenbaur, Waldeyer), in this manner : each osteoblast, by the peripheral portion of 
its cell-substance (Waldeyer), gives origin to the osseous ground-substance, while the 
central protoplasm around the nucleus persists with this latter as the nucleated bone-cell. 
The bone-cell and the space in which it lies become branched. For a row of osteoblasts 
we then find a row of oblong or round territories, each composed of matrix, and in it a 
branched nucleated cell. The outlines of the individual territories are gradually lost, and 
we have then a continuous osseous lamina, with its bone cells. The ground-substance 
is from the outset a network of fibrils, it is at first soft, but soon becomes impregnated 
with inorganic salts, this process commencing at the ' point of ossification.' The bone 
cells, with their processes, are situated in corresponding lacunae and canahcuh, just as 
in the adult osseous substance. 

Intermembranous Bone. 
The tegmental bones of the skull and the bones of the face are developed, without 
the intervention of cartilage, directly from a membrane which, in its structure and its 
function, corresponds to the future periosteum of those bones. This membrane, like that 
of long bones, consists of an inner osteogenetic and outer fibrous portion, the osteogenetic 
portion containing the same elements as in former cases, viz. blood-vessels and nucleated 
cells. As development proceeds there appears a reticulum of fibres, or bundles of fibres, 
in the meshes of which these cells are contained. The formation of bone from this 
periosteum is in all respects identical with that of the periostal bone, described on a 
former page. 



PERIOSTAL BONE. 65 

1st Stage. The cells of the osteogenic layer increase in number and form 
more or less continuous groups. These cells, osteoblasts, produce osseous substance 
(matrix and bone corpuscles) in the manner described above, and thus give origin 
to a more or less dense plexus of young bone-trabecuke, which, by new layers of 
osteoblasts, gradually increase in thickness. Many of these terminate or rather 
originate in the osteogenetic layer with pointed extremities ; their ground-substance 
is everywhere connected with the fibres of the osteogenetic layer, and their surface 
covered with osteoblasts. We have here, therefore, to deal with the identical ap- 
pearances that we described of the formation of the outer or periostal bone of the 
shaft of long bones. The production of the plexus of osseous trabecule by the 
osteoblasts starts from the 'points of ossification,' and gradually extends towards the 
periphery, the plexus being closest and the trabecule thickest in the former locality. 

But the plexus of trabecular extends also into the depth, new trabecular being con- 
stantly formed in the osteogenetic layer. The result is, here just as in the shaft of long 
bones, that we find at a certain time underneath the (osteogenetic layer of the) periosteum 
a thicker or thinner stratum of spongy bone, the meshes (Haversian spaces) of which 
contain a vascular and cellular tissue, viz. marrow, derived from, and in continuity with 
the osteogenetic layer of the periosteum. 

2nd Stage. Portions of the osseous trabecular are absorbed, osteoporosis ; during 
and after this process concentric lamellar are formed by the marrow in the Haversian 
spaces, which hereby become reduced to the Haversian canals. The systems of concentric 
lamellar are separated by the unabsorbed remains of the osseous trabecular of the 
primary spongy bone, these acting now as the interstitial or ground-lamellar. We 
have thus compact substance formed from the spongy bone. 

The process of osteoporosis and the formation of compact substance embraces the 
inner and middle parts, that is those that have been formed first; the superficial layers 
next the periosteum being still in the young state of spongy bone. 

We see, then, that the formation of intermembranous bone, as in the tegmental 
bones of the skull and the bones of the face, is in every respect the same as the forma- 
tion of periostal bone in all other bones. 

Comparing, for instance, a section of the embryonal lower jaw (horizontal portion) 
or of the embryonal parietal bone with one through the middle of the shaft of an 
embryonal long bone, at a stage when all endochondral bone has disappeared in the 
central marrow cavity, and when the bone present is entirely periostal bone, it is impos- 
sible to distinguish the two by their histological characters, both being identical in 
development and structure. 



l 2 



66 ATLAS OF HISTOLOGY. 

From the foregoing description it is clear that the development and growth of bone 
in length and thickness is essentially a process of apposition of new layers or new 
masses of osseous substance, as had been maintained by experimenters like Hunter, 
Flourens, Duhamel, Oilier, and others, against Volkmann, Wolf, and others ; the last- 
named observers regarding growth of bone due to interstitial enlargement of osseous 
matter once formed. Osseous substance once formed, undergoes only slight interstitial 
growth, as is proved by the slight change of distance of the bone corpuscles at different 
ages (Ruge). 



In several instances absorption has been mentioned in connection with the different 
stao-es of development of bone. As long as bone grows there is also absorption 
going on in some place or other. In long bones there is a constant absorption of 
bone near the marrow cavity as long as the periosteum continues to produce new 
layers of bone — that is to say, as long as the bone grows in thickness. The absorption 
of compact substance next the marrow cavity proceeds in a manner contrary to 
that of the formation of it ; the concentric lamellae, which are the parts last formed, 
succumb first ; hereby the Haversian canals are widened, and are again transformed 
into Haversian spaces ; after the disappearance of the concentric lamellae the intersti- 
tial lamellae are absorbed, and the Haversian spaces become lost in the central marrow 
cavity. And a similar process occurs in the conversion of compact into spongy bone, as 
exemplified in the diploe of flat and short bones. Absorption of bone is also present in 
the spongy bone of the apophyses and the extremities of the diaphysis of the adult 
long bones, while these continue to grow in length. Just as in the embryonal spongy 
bone, so also in the spongy bone formed in the adult in the places just named, greater 
or smaller portions of the osseous trabecular, first formed, are absorbed, and replaced by 
lamellar bone substance. 

Many bones possess on their surface, underneath the periosteum, larger or smaller, 
deeper or shallower, circular, oblong, or irregular pits — Howship's lacunae — which owe 
their origin to absorption of bone. Absorption of osseous substance is a never-failing 
companion of many diseases of bone. The absorption of osseous substance is in most 
instances (embryonal and adult) associated with the presence of the multinuclear giant 
cells (Kolliker) mentioned on former pages, and being regarded as the chief agencies 
of absorption, are called Osteoclasts (Kolliker). Osteoclasts have been noticed also 
in absorption of bone under pathological conditions (Wegner, M orison, and others). 
But in the course of absorption of calcified cartilage, as during the development of 
endochondral bone in general, and especially at the extremities of the shaft of long bones, 



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ABSORPTION OF CARTILAGE AND BONE. 67 

we find that this is also supported by multinuclear giant cells ; they may be then 
appropriately called Chondroclasts. 

The solution and absorption of calcified cartilage and osseous substance cannot be explained 
merely by the action of the blood-vessels of the marrow, for the simple reason that the insoluble 
lime-salts of those tissues cannot be dissolved by the alkaline plasma exuded from the blood- 
vessels. To convert those salts into soluble matter requires an acid which, in all probability, is 
formed in loco ; and it is equally probable that the osteo- and chondroclasts are the means 
by which it is produced. As a matter of fact, these giant cells comport themselves in microche- 
mical respects as if of acid reaction. 

But not all multinuclear giant cells, found at the different places where absorption 
of calcified cartilage or of osseous substance occurs, are merely destructive agents ; for 
there are other places where they can be shown to be concerned in the formation of 
osseous substance, just like the ordinary uni-nuclear osteoblasts. And the multinuclear 
giant cells are indeed only derived from osteoblasts, some of them having undergone an 
exceptional increase in size, and their nucleus a repeated division. The giant cells 
connected with absorption are generally on one side of a more or less opaque appearance, 
and transversely striated ; with this part they are closely applied to the surface that is to 
be absorbed. 

PLATE XII. 

Figs. I. and IV. drawn under a magnifying power of about 45 ; fig. II. under one 
of about 1 80 ; and fig. III. of 90. 

Fig. I. Transverse section of shaft of tibia of fcetal kitten. The section had been 
stained first in carmine and then in hematoxylin. All bone represented in this and the 
following two plates had been first macerated in chromic acid to deprive it of its inor- 
ganic salts. 

a) Periosteum, showing the outer fibrous and inner osteogenetic layer. 

6) Fcetal spongy bone, produced by the periosteum. The osseous substance is of a 
pink colour, and contains numerous bone corpuscles, of which only the nuclei are 
here shown. The trabecular next the osteogenetic layer are the most recently formed, 
they are covered with a regular epitheloid layer of osteoblasts. The cavities of the 
spongy bone, the Haversian spaces, contain a vascular and cellular tissue, which on the 
one hand passes into the marrow of the central cavity, and on the other is continuous 
with the osteogenetic layer of the periosteum. 

c) The central or marrow cavity containing blood-vessels filled with blood, and 
numerous marrow cells. In it are still left the (unabsorbed) remains of the endochondral 



68 ATLAS OF HISTOLOGY. 

spongy bone, whose trabecule still include thin (linear) masses of calcined cartilage, 
stained deeply purple. On the left side of the section there is still to be seen a 
definite boundary between the periostal and endochondral bone ; in the right part of 
the section all endochondral bone has disappeared. 

Fie-. II. From a section through a dried frontal bone (not macerated) of man, 
showing the lamellar arrangement of the osseous ground-substance, and between the 
lamella? the oblong lacunce of the bone corpuscles with their numerous canaliculi. 
The bone having been dried, the bone cells and their processes contained in the lacunae 
and their canaliculi have disappeared, the latter being now filled chiefly with air. In 
transmitted light they therefore appear black, the ground-substance being transparent; 
and in reflected light the lacunae and canaliculi are bright, while the ground-substance 

is dark. 

Fig. III. From a transverse section through part of shaft (compact substance) of 

dried radius (not macerated) of man. 

a) Systems of concentric or Haversian lamellae ; between the latter are seen the 
lacunae of the bone corpuscles ; their canaliculi pass transversely through the lamellae, 
and open into the central or Haversian canal. 

b) Interstitial or ground-lamellae, and between them the bone corpuscles. 

The Haversian canals, owing to the bone having been dried, are filled with air and 
dry remains, and appear therefore black. 

Fig. IV. From a longitudinal section through the head of humerus and adjoining 
portion of shaft of foetal kitten ; the section had been stained first in carmine and then 
in hematoxylin. 

a) Part of epiphysis next the intermediary cartilage ; it is spongy bone, of which 
here only a (qw broad trabecular (stained pink) are shown ; they still include consider- 
able masses of unabsorbed calcified cartilage, stained deeply in logwood. The bone 
corpuscles are indicated by their minute nuclei. Between the trabeculae of this 
spongy bone is a vascular and cellular marrow, not detailed in this figure. 

6) Hyaline cartilage, the remains of the foetal cartilaginous epiphysis; on this 
cartilage encroaches the spongy bone of the epiphysis ; the cartilage next to the 
part (a) is more transparent, owing to the cartilage lacunae being enlarged ; the cartilage 
ground-substance of this zone becomes gradually calcified, and therefore stains deeply 
in logwood. 

c) Intermediary cartilage ; the cartilage cells are arranged in longitudinal rows. 

d) Extremity of the shaft ; the cartilage near it is more transparent, owing to 
the lacunae being enlarged ; these lacunae gradually merge into the marrow spaces of 
the spongy substance of d y while the cartilage cells disappear. The ground-substance 



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INTERMEDIARY CARTILAGE. 69 

of the cartilage is here calcified (stained deeply in logwood). Numerous osteoblasts 
cover the trabeculae in the region d } and on some of these there are already indications 
of (pink) osseous substance. 

c) Section through part of a cartilage-channel, containing cellulo-vascular tissue 
derived from the perichondrium (periosteum) as a periostal process of Virchow; see a 
former page. 

PLATE XIII. 

Figures V. VI. and VII. drawn under a magnifying power of about 350; 
fig. VIII. under one of about 450. All figures represent preparations of bone 
that had been macerated in chromic acid, and hereby deprived of its inorganic 
matter. 

Fig. V. From a transverse section through the shaft of tibia of fcetal kitten, stained 
first in carmine and then in hematoxylin ; from a similar preparation as fig. I. of the 
previous plate. 

a) Fibrous layer of periosteum. 

5) Osteogenetic layer of periosteum, containing nucleated cells in a plexus of fibres. 
Towards the depth the cells become larger in size, and some of them more or less 
drawn out in processes. These cells are the osteoblasts, in the act of forming osseous 
substance. 

c) Spongy bone formed by the periosteum, periostal bone. In its matrix, stained 
pink, are contained the branched bone corpuscles. The meshes of this bone, viz. the 
Haversian spaces, contain numerous osteoblasts. 

d) Endochondral formation of bone. The unabsorbed calcified cartilage trabeculae 
(stained blue) become gradually covered with thinner or thicker laminae of osseous 
substance (stained pink), and with numerous osteoblasts. In one marrow cavity is 
shown a blood-vessel ; all the marrow cavities contain numerous cells. 

e) Distinct boundary between the endochondral and periostal bone. 

Fig. VI. From a longitudinal section of femur of rabbit, through the region in 
which the extremity of the shaft is in contact with the intermediary cartilage. The 
vessels of the bone had been injected with Berlin-blue, and the section had been stained 
first in carmine, then in hematoxylin. This figure illustrates the growth in length of 
the shaft of a long bone. 

a) Intermediary cartilage. The cartilage cells are somewhat flattened and ar- 
ranged in characteristic longitudinal rows. 



7 o ATLAS OF HISTOLOGY. 

6) The transparent region of the large cartilage lacunae. The cartilage cells are 
very transparent and swollen up ; the cartilage ground-substance is partly calcified. 

c) The region in which the cartilage lacunae have become confluent with the 
marrow cavities, the cartilage trabecule being calcified, and more or less covered with 
osteoblasts ; into this region extend the capillary blood-vessels, terminating here as 
loops. Among the uninuclear osteoblasts there are a few multinuclear giant cells, which 
probably act here as chondroclasts. 

In the depth of this, and in the next region, d } the calcified cartilage trabecular 
become more or less reduced in thickness, and covered with osseous substance (stained 
pink). This is more marked the further away from the intermediary cartilage. 

Fig. VII. From a similar preparation as that of the preceding figure, only more 
highly magnified, to show a large trabecula of calcified cartilage taken somewhere 
between c and d of the preceding figure. 

The upper part of the calcified cartilage, stained faintly blue, is covered with mul- 
tinuclear giant cells. These being placed on cartilage which is to be absorbed are very 
probably the instruments of absorption, and hence deserve the name of chondroclasts. 
Towards the depth, that is, towards the shaft, the cartilage becomes covered with 
osseous substance, stained pink, and numerous osteoblasts. 

Fig. VIII. From a longitudinal section through the spongy bone of shaft, but not 
far from the intermediary cartilage of femur of fcetal kitten, to show the formation of 
osseous substance on the trabecular of calcified cartilage represented in the preceding 
two figures. The section had been stained first in carmine and then in logwood. 

a) A marrow cavity containing a blood-vessel (with blood corpuscles), and a 
few marrow cells ; many of these had been accidentally removed from the prepara- 
tion. 

b) Calcified cartilage, stained faintly blue. It is covered either with isolated or 
continuous masses of osseous substance, stained pink. The isolated masses consist of 
a matrix of fibrils, a small cavity, and in this a nucleated cell ; this latter ought to be 
represented more branched. Each of these isolated masses is derived from one osteo- 
blast, of which the peripheral portion has become converted into the osseous matrix, 
while the part of the cell-substance immediately around the nucleus persists as the 
nucleated bone cell, this becoming at the same time branched, and separated from the 
matrix by a similarly branched lacuna. As development proceeds, these isolated masses 
become confluent into more or less continuous laminar. 



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DEVELOPMENT OF BONE IN MEMBRANE, 



7i 



PLATE XIV. 

Figures IX. X. and XI. are drawn under a magnifying power of about 350 ; the 
other two under one of about 250. 

Fig. IX. From a transverse section through part of lower jaw of human foetus, 
next the external periosteum. The section had been stained first in carmine and then 
in haematoxylin. The jaw was in the stage of spongy bone. 

a) Fibrous layer of periosteum. 

b) Osteogenetic layer of periosteum. 

c) Osseous substance, stained pink, and containing numerous bone corpuscles. 
Next the periosteum the trabecular are covered with an epitheloid layer of osteoblasts • 
the two pointed projections of osseous substance into the osteogenetic layer are parti 
just in the act of formation. 

d) Haversian spaces, marrow cavities containing marrow ; some of the cells are 
arranged as osteoblasts on the surface of the osseous substance. 

Fig. X. A small isolated mass of bone next the periosteum of lower jaw of human 
foetus of a similar specimen as the one mentioned in the foregoing figure. 

a) Osteogenetic layer of periosteum. 

b) Multinuclear giant cells; the one on the left side acting here probably like an 
osteoblast. The large giant cell in the middle of the upper margin of the osseous 
substance has an opaque lower margin vertically striated. With this margin it rests in 
a small Howship's absorption pit. Above c the osteoblasts are seen to become gradu- 
ally surrounded by osseous matrix, and are thus converted into bone corpuscles. 

Fig. XI. From a section through osseous substance of vertebral bone of adult 
mouse ; the preparation had been stained in chloride of gold. 

Nucleated bone cells and their processes contained in the bone-lacunae and their 
canaliculi respectively. 

Fig. XII. From a transverse section through part of lower jaw of foetal kitten, 
next the inframaxillary canal ; the section had been stained first in carmine and then in 
hematoxylin. 

a) Periosteum lining the inframaxillary canal. 

b) Layer of multinuclear giant cells ; each of them situated in a small pit, but close 
to the osseous substance. 

These pits correspond to the absorption pits, or Howship's lacunae. The giant 
cells act here as bone-absorbers, osteoclasts. The margin of these osteoclasts resting on 

M 



ATLAS OF HISTOLOGY. 
1 b„„e is opacue, ,„<, „,ore or less «„«., vertically striated ; .Iris appe— is not 

represented in the figure. 

A Oseous substance. 

' , i mo nt Inwer iaw of fcetal kitten. The preparation 

Fig. XIII. From the spongy bone ot lowei jaw 01 

had been stained in carmine only. 

a) Periosteum. . , 

< Trabecule of fetal bone, connected by smaller or larger bundles of fibres wh 
the fibrous matrix of the periosteum. These bundles of fibres are the rudunents of the 
perforating fibres of Sharpey. On the surface of the osseous trabecular are seen 
nucleated osteoblasts forming osseous substance. 




CHAPTER X. 

UNSTRIPED MUSCLE. 

The tissue of unstriped muscle has a wide distribution in man and the other vertebrates. 
Large masses of it are present, in the shape of bundles or continuous coats, in the 
oesophagus, stomach, small and large intestine, trachea, bronchi and infundibula of lunw 
pelvis of kidney, urethers, bladder and urethra, prostate, epididymis, vas deferens, 
vesiculae seminales and ejaculatorii, and corpora cavernosa ; ovary, Fallopian tube and 
ligamenta lata, uterus and vagina ; in the arteries and many veins, in the semi-lunar 
valves of the heart and some lymphatic trunks; the gall-bladder, ductus hepaticus, 
cysticus and choledochus ; the duct of the parotid, submaxillary, and pancreas glands ; 
the capsule and trabecular of the spleen, and, in some mammals, also those of lymphatic 
glands ; occasionally in the serous membranes, in the muscles of the hairs (arrector pili) 
in sweat glands and ceruminous glands ; the sphincter and dilatator pupillse, the tensor 
chorioides, and the muscle of Miiller in the orbital fissure are unstriped muscle tissue. 

The elements of this tissue are elongated, spindle-shaped, or bandlike cells of 
various lengths, each with an oblong nucleus. They are aggregated into smaller or 
larger bundles, and these again into groups or continuous membranes. 

The muscle cells within a bundle are imbricated and held together by a semi- 
fluid, transparent, albuminous, interstitial or cement substance, identical with the 
substance uniting epithelial and endothelial cells, mentioned in a former chapter. But 
there are flattened connective-tissue cells to be met with in this cement-substance, and 
also now and then a few connective-tissue fibres. Both these tissues, viz. connective- 
tissue cells and fibres, represent the endomysium. The tissue surrounding or separating 
the individual bundles is fibrous-connective tissue of the ordinary description, and 
represents the perimysium. The endomysium is continuous with the perimysium. 

The bundles of unstriped muscle fibres often are connected with one another in the 
form of a plexus, larger bundles dividing into smaller ones, and then again reuniting. 

The unstriped muscle cells in a bundle are pressed against one another, appearing 
therefore more or less polyhedral in transverse section. The individual cells consist in 
the fresh state of a transparent more or less distinctly longitudinally striated substance 
(Arnold, Klein, Flemming, Ranvier), and their transverse section presents accordingly 
a finely and uniformly dotted appearance. 

N 



ATLAS OF HISTOLOGY. 
74 

Each muscle cell consists of the following parts (Klein) :-(a) of a fine sheath, 
probably elastic, which possesses transverse linear thickenings-these are especially 
distinct when the muscle cell or part of it is in a contracted state (see below) ; (5) a 
central bundle of fibrils representing the contractile substance or the core ; (*) an oblong 
nucleus which, within a membrane, includes a fine network (Flemming, Klein). This net- 
work anastomoses at the poles of the nucleus with the bundle of fibrils of the core (Klein). 
The position of the nucleus varies in different muscle cells ; as a rule it is in about 
the middle of the long axis of the cell, but there are many instances in which the 
nucleus is nearer to one extremity than to the other. As a rule the nucleus is contained 
in the thickest part of the cell. In muscle cells treated with hardening reagents the 
nucleus is often shrunk, so that its outline becomes wavy and notched. At the ex- 
tremities the muscle cell is drawn out either into a longer or shorter fine point pushed 
in between the neighbouring cells. In some instances both extremities are branched, 
being split into two or more longer or shorter processes. Muscle cells with branched 
extremities may be found in isolated examples in most instances, but in the arteries 
and veins they are very numerous. 

Unstriped muscle tissue varies in different organs as regards the length and 
thickness of its cells. The longest and thickest muscle cells are found in the intestines, 
the shortest in the arteries, the thinnest in the sweat-gland tubes. 

Unstriped muscle tissue is richly supplied with nerves. These will be specially 
treated in a future chapter on the termination of motor nerves. The blood-vessels, like 
those of other organs, consist of afferent artery, efferent vein or veins, and a network of 
capillary vessels. These latter are intrafascicular, they run parallel to the long axis of 
the bundles, and anastomose by transverse branches into a network. But the number 
of capillary blood-vessels is on the whole small if compared with the number present in 
striped muscle tissue, 



75 



CHAPTER XI. 

STRIPED MUSCLE FIBRES. 

All muscles of the skeleton, the heart, and diaphragm, the muscles of the oral cavity, 
pharynx and larynx, and part of oesophagus, the external muscles of the eye-ball, the 
muscles of the middle and outer ear, the sphincter vesicae, part of the muscles of the 
prostate, &c, consist of striped muscle fibres. These are long cylindrical fibres of 
various thickness, showing a regular transverse striation, due to various discoid dements 
entering into the constitution of the individual cylinders. The fibres are aggregated into 
smaller groups, bundles, and these again into large fasciculi, which form part of an 
anatomical muscle. Ordinary fibrous-connective tissue separates or surrounds the in- 
dividual bundles as perimysium ; from this pass minute bundles of connective tissue, with 
connective-tissue cell plates, into the muscle bundles between the individual muscle 
fibres as endomysium. Amongst the cells of the endomysium the plasma cells are 
especially noticeable. See Chapter IV. p. 27. 

Each muscle fibre, when viewed in the fresh and living but resting state along its 
long axis, shows : — (a) transverse broad dim bands of a highly refractive substance, 
alternating with (b) narrow bright bands of a less refractive substance. Both are due to 
discs placed vertically to the long axis. As will be seen presently, the former alone 
represent the contractile portion of a muscle fibre, and may be therefore called the 
contractile discs : the latter, being merely interstitial substance, may be spoken of as 
interstitial discs (Rollett). During contraction, viz. the parts through which a contrac- 
tion wave is just passing, the former become thinner in the long axis of the muscle 
fibre and transparent, the latter more opaque. But while the contractile disc becomes 
thinner along the long axis of the fibre, it, and consequently also the muscle fibre, 
becomes thicker in a transverse direction. When a muscle fibre that in the fresh and 
living state merely shows a differentiation into the above transverse discs, dies sponta- 
neously or in consequence of hardening reagents, it changes its aspect, inasmuch as it 
becomes, in addition, longitudinally striated, owing to the appearance of longitudinal, fine. 
apparently linear masses of a clear bright substance, gradually increasing in amount. 
Hereby each dim contractile disc becomes differentiated, as it were, into thin oblong 
rods, the sarcous elements of Bowman, each of which is the length of the disc. 

The sarcous elements represent the anatomical elements of the contractile disc. 

N 2 



_ 6 ATLAS OF HISTOLOGY. 

in the fresh and living state they are prismatic corpuscles arranged side by side ; those 
forming one disc are in immediate contact with one another, and being all of the same 
optical refractive power, no differentiation can be perceived, and the disc appears there- 
fore quite homogeneous. But when, either spontaneously during life, or after death and 
reagents the sarcous elements shrink (coagulate), they become separated from one another, 
and a transparent interstitial fluid substance, pressed out from the sarcous elements 
(En^elmann), is now seen occupying the crevices between them. The above clear bright 
lines & correspond to this substance. They contain in many eases rows of granules 
(Henle, Kolliker). The interstitial substance corresponds in appearance and chemical 
respects to the interstitial transverse disc above mentioned, and both represent the albu- 
minous substance discovered by Kuhne, and called by him myosin. A longitudinal 
series of sarcous elements (one abreast) represents a so-called primitive fibril. A muscle 
fibre may therefore be regarded as composed either of transverse discs or of longitu- 
dinal fibrils, according to whether we look upon the sarcous elements as being ar- 
ranged sideways or endways. Certain reagents possess the property of bringing out 
more prominently the one or the other arrangement. Thus muscle treated with alcohol 
shows generally the arrangement of the sarcous elements into fibrils more strikingly 
than in transverse discs, whereas the reverse is the case with hydrochloric acid. 

The length of the sarcous elements, or what amounts to the same, the length of a 
contractile disc, or the breadth of the striation, varies considerably in different animals 
and also in different muscles of the same animal ; it is much greater in insects than 
in vertebrates. Equally variable in thickness is the interstitial disc. 

The thickness of the individual muscle fibres is subject to great differences in 
different animals and in the muscles of one and the same animal, varying between the 
fine fibril of the thorax muscle of hydrophylus piceus, representing almost a single 
row of sarcous elements, to the tremendous muscle fibre of the claw of a lobster. 

When viewing a transverse section through fresh and living muscle, the muscle 
substance appears at first homogeneous and of a dim aspect ; gradually there appear 
shorter or longer lines of a clear bright substance ; these anastomose, and are so arranged 
that the muscle substance seems divided into relatively large polygonal areas. The 
clear lines are in some places of some muscle fibres greatly enlarged, owing to the 
presence in them of a nucleated cell, or muscle corpuscle (see below). The numbers of 
clear lines gradually increase, and consequently the size of these areas decreases, until we 
arrive at a permanent subdivision of the transverse section into small polygonal areas of 
dim substance, each corresponding to one sarcous element prism viewed endwise (Cohn- 
heim's fields) ; the clear lines are the interstitial substance, mentioned above as gradually 
appearing between the sarcous elements. The individual sarcous elements do not, 



STRUCTURE OF STRIPED MUSCLE FIBRES. 77 

however, present a homogeneous aspect when thus viewed endways, but appear 
granular, this being probably merely the expression of minute longitudinal fibrils (Kolliker). 
The transverse section of a muscle fibre, after hardening, shows the sarcous elements 
(Cohnheim's fields), or primitive fibrils, very often greatly shrunk, and therefore like 
small dots, the interstitial substance of course appearing greatly increased accordingly. 

Besides the structural differences described hitherto, there are other minute elements 
entering the constitution of a muscle fibre : these can be perceived already in the fresh 
and living state, but better after certain reagents. These structures are : {a) a hyaline 
sheath, the sarcolemma : this is a transparent structureless elastic sheath of great resist- 
ance ; it surrounds the contents of the muscle fibre like a cuticle. (b) In connexion with 
the sarcolemma are transverse fine membranous septa, stretching right across the 
muscle fibre at regular intervals : these septa are the membranes of Krause ; they are 
homogeneous, elastic, but show less resistance (Engelmann) than the sarcolemma with 
which they are intimately connected. By these transverse septa the muscle fibre is 
divided into numerous equal-sized cylindrical compartments, muscle-compartments of 
Krause, each of which possesses the breadth of the whole muscular fibre. Each com- 
partment contains one dim contractile disc, mentioned above. Now, the membranes of 
Krause are so placed that each of them passes right across the middle of an interstitial 
disc from one side of the muscle fibre to the other; hence each interstitial disc is divided 
into two halves, the lateral discs, each of these belonging to different (adjacent) com- 
partments. 

We may then summarise the structure of a striped muscle fibre thus : 

i) The framework. This consists of: (a) Sarcolemma ; and (b) Krause s membranes ; 
hereby the fibre is divided into muscle compartments. 

2) The muscle-substance : (a) each muscle compartment contains one broad dim con- 
tractile disc, highly refractive, composed of prismatic rods, sarcous elements ; (b) a narrow 
transparent lateral disc placed at each end of the contractile disc, and consequently at the 
side of Krause's membrane. According to Hensen and Engelmann, a transparent 
transverse thin ( median disc' divides the contractile disc into two ; but this appearance 
is found only under exceptional conditions (see below). 

In some muscle fibres, especially in some fibres of insect muscle, we find each 
lateral disc containing, in the transverse diameter, a row of bright granules, so placed 
that each granule corresponds to the end of a sarcous element. But they are not of 
constant occurrence, being often absent (Krause). According to Schafer, who regards 
them as constant features, they are the knoblike ends of thin rodlike elastic elements 
which constitute the dim disc. 

These granules form the 'granular layer' of Flogel. In some muscle fibres this 



7 S ATLAS OF HISTOLOGY. 

granular layer is in the centre of the lateral disc ; in others, it is nearer the con- 
tractile disc, and still in others nearer the Krause's membrane. 

The striped muscle fibres contain numerous oblong more or less flattened nuclei, 

each embedded in a thin more or less branched film of protoplasm. Each nucleus 

contains a uniform network, intranuclear network. Both nucleus and protoplasm form 

the muscle cell or muscle corpuscle of Max Schultze. In the muscle fibres of higher 

vertebrates, except the heart, the muscle corpuscles are, as a rule, situated on the surface 

of the muscle substance, but underneath, not in, the sarcolemma. In the muscle fibres of 

amphibian animals and insects we find them sometimes only in the centre of the fibres 

(Weismann, Kolliker). In birds (pigeon and fowl, Rollett) both conditions are met with. 

The number of muscle corpuscles varies greatly in different muscle fibres ; they are 

always more numerous in young, developing, or growing fibres (see below). 

Muscle fibres differ in colour, some being red, others pale. In mammals this is 
owing, in some instances, to well-defined structural differences (Ranvier). Comparing a 
red muscle, e.g. semitendinosus, of rabbit with a pale one, adductor magnus or vastus 
interims of rabbit, Ranvier finds the fibres of the red more longitudinally, those of the 
pale ones more transversely striated ; the former possess a much greater number of 
muscle corpuscles than the latter ; the red fibres contract slower than the pale ones, and 
the latter return much quicker to their state of rest. But these differences are not of a 
constant nature, inasmuch as, according to E. Meyer, the red muscles of other parts and 
in other animals (flexor digitorum com. and masseter of rabbit, red muscles of other 
rodents) do not show any different characters from the pale ones. In some instances 
(silurus) the red fibres of the red muscles are thinner than those of the pale ones 
(Ranvier), in others (rabbits) just the reverse is the case (E. Meyer). The more a* 
muscle works the deeper its colour (E. Meyer). 

The muscle fibres of some organs, tongue (Remak, Ripmann, Kolliker, Salter, and 
others), facial muscles (Huxley, Busk, and others), and especially heart, are branched, 
either repeatedly but without anastomosis of the branches, as in the former, or they are 
arranged in a network, as in the latter. 

The muscle fibres of the heart show the following peculiarities: (i) they do not 
possess any sarcolemma ; while ordinary striped muscle fibres in transverse section, either 
fresh or after reagents, show a well-marked and sharp limiting membrane, the sarcolemma, 
those of the heart are limited by their muscle substance itself. (2) A transverse section 
through heart muscle differs also in other respects from that of ordinary muscle ; 
while ordinary muscle shows the transverse sections of its muscle fibres as round or 
oval bodies more or less pressed against one another, and differing in size within 
moderate limits, those of the heart, on the other hand, are of various sizes, and being 



MUSCLE FIBRES OF THE HEART. 79 

repeatedly branched, are irregular in shape and size, according to whether the transverse 
section is taken from a part of the fibre at the point of branching or from a part above or 
below it. (3) The muscle corpuscles of the fibres of the heart are invariably situated in 
or about the centre of the fibres (Donders) ; the number of the muscle corpuscles is 
relatively great, and the chances therefore are that in a transverse section the greater 
majority of fibres are cut through the muscle corpuscle. Corresponding to the individual 
muscle corpuscles the fibres appear, under certain conditions, subdivided into oblong cylin- 
drical blocks (Aeby, Eberth, and others), straight at their ends, or divided according to 
whether they belong to an undivided or dividing portion of a fibre. 

Muscle fibres have only a limited length; they terminate or originate respectively 
either within the bundle (Rollett) or in a tendon. In the first case, the contents of the 
fibre terminate abruptly in a conical shape, and the sarcolemma, having collected into 
a fine filamentous structure, loses itself in the connective tissue separating the muscle 
fibres. In the second case, a muscle fibre passes into a bundle of fine connective-tissue 
fibrils in either of two ways : (a) the contents of a fibre terminate conically, and the sarco- 
lemma appears to pass on a tendon bundle of connective-tissue fibrils, or (6) the muscular 
contents themselves seem to be continued, apparently without interruption, into the ten- 
don bundle. 

The muscle fibres near their termination or origin respectively become gradually 
reduced in diameter, hence their shape is that of a spindle (Herzig, Biesiadecki, Krause, 
Weismann, and others). In a given transverse section through a bundle of striped 
muscle fibres we therefore find the muscle fibres of various diameters, some two and 
three times as thick as others ; this is explained by the fibres being spindle-shaped, 
thickest in the middle parts, and tapering towards the termination. 

According to Kolliker, in small muscles, as in the small muscles of the extremities 
of bat, muscles of frog, all individual fibres extend the whole length of the muscle ; but 
in large muscles, according to Herzig, Krause, and others, the length of the fibres does 
not exceed 1 i to 2 inches. 

At an early stage of embryonal life elongated spindle-shaped cells are transformed 
into striped muscle fibres, each such cell giving origin to a muscle fibre (Remak, Weis- 
mann, Kolliker, and others). These spindle-shaped cells, at first thin and small, enlarge 
to a very great extent, and their nucleus undergoes repeated division. The cell-substance, 
beginning from the periphery, becomes differentiated into the striate muscle substance, viz. 
sarcous elements and interstitial substance (Remak, Weismann, Fredericq, and others). 
What remains of the original protoplasm u around the nuclei — more distant from 
each other as development proceeds — represents a muscle corpuscle. The sarco- 
lemma is developed from nucleated cells different from the muscle corpuscles (Calberla, 



8o ATLAS OF HISTOLOGY. 

Wolff) ; in the adult fibres no trace of the nuclei of those cells is to be found in the 
sarcolemma. The younger the muscle fibre the more numerous the muscle corpuscles, 
and the greater the amount of protoplasm around them. When muscle fibres undergo 
increase in thickness and number, as during prolonged and systematic muscular exercises, 
we find the muscle corpuscles taking an active part therein ; they enlarge and multiply, 
and the greater part of their substance is converted into muscle substance proper ; the 
mode of this transformation is the same as in the embryo. 

Thus we find many muscle fibres of the diaphragm of young as well as adult 
mammals (dog, rabbit, guinea-pig) possessing the character of growing fibres, viz. 
numerous and large muscle corpuscles sometimes forming on the surface of the muscle 
tissue proper, but underneath the sarcolemma, a more or less continuous layer of poly- 
gonal or square cells of various sizes, each with one or several nuclei. The protoplasm 
of these cells is gradually converted, and hence passes insensibly, into the striated muscle 
substance. The great number and size of the muscle corpuscles in some of the fibres 
of the diaphragm, as compared with those of the fibres of another muscle, e.g. quadratus 
lumborum, of the same animal, is not owing merely to the fact that the diaphragm being 
a red muscle its fibres possess many more muscle corpuscles than those of the quadratus 
lumb., which is a pale muscle ; not all the fibres of the diaphragm possess a great abun- 
dance of muscle corpuscles, and those that possess it do so much more conspicuously 
than the fibres of other red muscles (semitendinosus) of the same animal. 

It is probable that the character of many muscle fibres of the diaphragm, just de- 
scribed, indicates a constant new formation and increase of thickness. Constant work 
necessitates constant waste, and very likely constant reproduction. 



The lymphatics and nerve-termination of striped muscle tissue will be described in 
the chapters on the Lymphatic and Nervous System respectively. 



Striped muscle tissue is richly supplied with blood-vessels, the arteries and veins 
being situated in the perimysium, the network of capillaries in the endomysium, between 
the individual muscle fibres. The capillary blood-vessels are very numerous, and run 
parallel with the muscle fibres ; they anastomose by short transverse branches, hence 
the meshes of the capillary network are preeminently of an elongated shape. In the 
red muscle of rabbit Ranvier demonstrated a peculiar condition of the minute veins and 
capillaries, these vessels being possessed of sinuous and spindle-shaped dilatations, 
owing probably to the almost permanent contraction of these muscles (E, Meyer). 

Brucke was the first to show that striped muscle fibres are doubly refractive, and 



■: , 




m 






«• 






















OPTICAL PROPERTIES OF STRIPED MUSCLE. 81 

that they comport themselves in this respect like positive uniaxial bodies (rock crystal), 
the optical axis being the long axis of the muscle fibres. 

But not all parts of a muscle fibre are doubly refractive, the sarcous elements 
(Briicke) and Krause's membrane (Engelmann) being anisotropous, the lateral disc 
isotropous. 

The sarcous elements are not the optical units, but must be considered as consisting 
of minute doubly refractive elements, disdiaclasts (Briicke). We have seen on a former 
page that also in morphological respects the sarcous elements are not of a homogeneous 
structure, but probably composed of minute fibrils (Kolliker). 



PLATE XV. 

Figures I. and III. are drawn under a magnifying power of about 180; figures II. 
and VIII. under one of about 450; and figures IV. V. VI. and VII. of about 300. 

Fig. I. Unstriped muscle cells of mesentery of newt ; the sheath with transverse 
markings is faintly seen. 

Fig. II. From a similar preparation as fig. I., showing that each muscle cell con- 
sists of a central bundle of fibrils (contractile part) connected with the intranuclear net- 
work, and a sheath with annular thickenings. The muscle cells show varicosities, 
probably owing to local contractions, and on these the annular thickenings are more 
distinct. The mesentery had been prepared with chromate of ammonia. 

Fig. III. Plexus of bundles of unstriped muscle cells of the pulmonary pleura of 
guinea-pig. 

Fig. IV. From a vertical section through the circular muscle coat of large in- 
testine of pig. The intestine had been hardened in chromic acid. From the con- 
nective tissue of the perimysium pass smaller and larger bundles between the individual 
muscle cells, shown here in transverse section. In many places the muscle cells have 
been removed (accidentally), and the interstitial substance is then seen as a honey- 
combed structure. Owing to the muscle cells being of considerable length, only few 
of them show a nucleus. The cells containing longitudinal fibrils (see above) appear in 
transverse section as if containing minute dots, these being the fibrils seen in section. 

Fig. V. From a vertical section through the circular muscle coat of small intestine 
of dog ; the intestine had been prepared with chromate of ammonia. The honey-comb 
interstitial substance is well shown, and in it a few nucleated connective-tissue cells. The 
muscle cells appear of different sizes in the transverse section, being spindle-shaped, and 
consequently some are cut through the thicker part, others nearer the fine extremity. 

o 



S 2 ATLAS OF HISTOLOGY. 

Fig. VI. Part of a striped muscle fibre of hydrophylus prepared with absolute 
alcohol. 

a. Sarcolemma. 

b. Membrane of Krause. 

Owing to contraction during hardening the sarcolemma shows regular bulgings. 
At the side of Krause's membrane is the transparent lateral disc. The chief mass 
of a 'muscular compartment' is occupied by the contractile disc, composed of sarcous 
elements. 

The substance of the individual sarcous elements has collected more at the extre- 
mity than in the centre, hence this latter is more transparent. The optical effect of 
this is that the contractile disc appears to possess a ' median disc.' 

Several nuclei (of muscle corpuscles) are shown, and in them a minute net- 
work. 

Fig. VII. A muscle fibre of hydrophylus prepared in the same manner as in fig. VI. 
The sarcolemma, to a great extent detached, shows the regular bulgings as in the pre- 
vious figure, but the membranes of Krause are not seen. 

Fig. VIII. Portion of a broken muscle fibre of hydrophylus, showing part of sar- 
colemma and part of Krause's membranes ; the contractile discs are being disintegrated 
into the constituent sarcous elements. 



PLATE XVI. 

Figures IX. X. XIV. a and b, and XVI. are drawn under a magnifying power of 
about 450 ; figures XI. and XIII. under one of about 300; figures XII. and XV. under 
one of about 150. 

Fig. IX. Transverse section through muscle fibres of human tongue. The muscle 
fibres appear in transverse section of different sizes, owing to their being more or less 
spindle-shaped ; each fibre is limited by a definite membrane, the sarcolemma. The 
muscle corpuscles are indicated by their deeply stained nuclei, situated at the inside of 
the sarcolemma. There are several connective-tissue corpuscles between the muscle 
fibres, belonging to the endomysium. Each muscle fibre shows the Cohnheim's fields, 
that is the sarcous elements in transverse section and separated by clear (apparently 
linear) interstitial substance. 

Fig. X. Transverse section through muscle of heart. The fibres are irregular in 
shape and size, owing to their being branched ; the muscle corpuscles are indicated by 
their nuclei, situated in about the middle of the fibres. 

Fig. XI. From a section through muscle of tongue of rat ; between and on the 










ft % * 

* i V 

* - ^ 

. ;, ■« * 



@ 



o 

























STRIPED MUSCLE FIBRES. S3 

muscle fibres are large uninuclear plasma cells. The structure of the fibres is the same 
as represented in figure VI. of the preceding Plate. 

Fig. XII. Striped muscle fibres viewed in longitudinal and in transverse sections, 
showing the blood-vessels injected with carmine gelatine. The blood-vessels have 
chiefly a longitudinal arrangement ; the left part of the figure shows both the muscle 
fibres and their capillary vessels more or less cut transversely. 

Fig. XIII. Two muscle fibres of hydrophylus, each passing into a tendon bundle 
of connective-tissue fibres. 

Fig. XIV. a and b, muscle fibres of diaphragm of adult guinea-pig. The muscle 
corpuscles are greatly enlarged and very numerous ; they are probably used here for the 
new formation of striated muscle substance. 

Fig. XV. Transverse section through several bundles of striped muscle fibres of 
tongue. The bundles are separated by vascular fibrous-connective tissue, perimysium ; 
this passes in between the fibres of the individual bundles. The clefts between perimy- 
sium and muscle fibres and between the individual muscle fibres themselves belong to 
the lymphatic system. 

Ficr XVI. Network of muscle fibres of heart of pig. 



o 2 



84 



ATLAS OF HISTOLOGY. 



CHAPTER XII. 

CEREBROSPINAL NERVES. 

The nerve trunks of the cerebro-spinal system, with the exception of the optic nerve, 
consist of the following structures (Axel Key and Retzius) : 

a) The cpineiirium, the common framework, is composed of bundles of fibrous- 
connective tissue arranged as larger or smaller trabeculae, which cross each other and 
thus form a more or less dense plexus. Between the bundles are the ordinary flattened 
more or less branched connective-tissue corpuscles, and in many places the coarsely 
granular plasma cells (Waldeyer), showing slight amoeboid movement. Fat-tissue, a 
plexus of lymphatics, and the numerous blood-vessels supplying the nerve trunk are all 
embedded in the connective tissue of the epineurium. 

b) In this common framework are embedded smaller and larger bundles of nerve 
fibres, nerve bundles. Each of these has its own special sheath of connective tissue, 
perineurium. This possesses a lamellar structure ; the lamellae consist of bundles of 
fibrous-connective tissue, and between them are the flattened connective-tissue cells, 
situated as it were in more or less continuous (interlamellary) lymph-spaces. The nerve 
bundle is a simple one if the nerve fibres are embedded in a uniform matrix, compound 
if in connexion with the perineurium thicker or thinner septa of connective tissue pass 
into the bundle, and thus separate the nerve fibres into two or more secondary groups. 

c) The nerve fibres within a nerve-bundle are separated from each other by 
endoneurium, viz. a more or less homogeneous substance containing numerous minute 
connective-tissue fibre-bundles and isolated fine connective-tissue fibres and flattened 
nucleated connective-tissue cells. The connective-tissue fibres are twisted and coiled 
round the individual nerve fibres in a complex manner, in some places forming a dense 
sheath around them. The endoneurium contains capillary blood-vessels having chiefly 
a longitudinal course. 

The endoneurium is accumulated occasionally on the surface of the nerve bundle, 
but inside the perineurium, as a special thinner or thicker peripheral layer. 

Between the inner surface of the perineurium and the nerve fibres themselves there 
are always to be found longer or shorter lymph-spaces lined by a layer of endothelium, 
and these are connected with lymph-spaces of the endoneurium passing in between the 
individual nerve fibres. The endoneural lymph-spaces have been injected by Axel Key 



DIVISION OF NERVE BRANCHES. 85 

and Retzius in connection with the lymph-spaces of the perineurium, and they have 
been shown by those observers to be so numerous that each individual nerve fibre 
appears surrounded by them. 

The microscopic branches of a nerve trunk consist of a simple or compound nerve 
bundle ensheathed in lamellar perineurium. The farther branches of these possess 
only a very delicate perineurium, which becomes the more delicate the further away 
from the original nerve bundle ; still further microscopic branches are reached where 
the perineurium has dwindled down to a single layer of cells, now forming a continuous 
endothelial membrane. Finally these branches split up into small groups and indivi- 
dual nerve fibres. 

Most of the nerve fibres contained in a nerve bundle are medullated ; they differ, as 
regards thickness, in different animals, in different nerve trunks, and even in the same 
nerve bundle of the same nerve trunk, some being thick, others medium-sized, and still 
others thin fibres (Kolliker). 

Each fibre possesses the following structure : (1) the axis cylinder, a solid soft pale 
central cylindrical structure, showing under certain conditions a longitudinal striation due 
to its being composed of minute longitudinal fibrils,— elementary fibrils (Max Schultze) 
—between these fibrils are seen minute granules, indicative of an interfibrillar granular 
cement-substance. 

(2) The medullary sheath, a thick bright sharply outlined (doubly contoured) fatty 
semifluid substance, forming a thick insulating cylindrical sheath around the axis 
cylinder; it coagulates very soon after death, and easily separates spontaneously, after 
pressure water, &c, into smaller or larger simple or compound spherical or globular 
droplike bodies. Under certain conditions (especially perosmic acid), it has been seen 
(Stilling, Schmidt, Lantermann, Kuhnt, and others) to consist of longer or shorter 
cylindrical sections which are imbricated with their margins. They have not been 
demonstrated, however, on all medullated nerve fibres, and not in the whole course of 
the same fibre. Each of these sections contains a reticulum (Stilling, Klein), a 
honey-combed framework ; in the meshes of this lies embedded the above-named bright 
fatty substance. The reticulum appears as a honey-comb only when looked at from the 
surface; when viewed in profile it seems to be composed of rod-like elements (Lanter- 
mann, MacCarthy); these are in reality the septa of that honey-comb seen sideways. 
This reticular honey-combed framework probably corresponds to the 'stroma of 
neurokeratin,' demonstrated by Ktihne and Ewald after digesting medullated nerves in 
trypsin. Between axis cylinder and medullary sheath is a very narrow space, periaxial 
space (Klebs), containing fluid albuminous cement-substance ; during life this space is in 
ordinary nerve fibres very minute, the axis cylinder being almost entirely in contact 






86 ATLAS OF HISTOLOGY. 

with the medullary sheath, but after shrinking of the axis cylinder the space becomes 
more distinct. After hardening reagents the above albuminous substance becomes 
coagulated, and then corresponds to a thin granular membrane surrounding the axis 
cylinder, described by Todaro and Schmidt. With nitrate of silver this layer appears 
occasionally as if composed of transverse bands or rings (Axel Key and Retzius), and 
may thus appear as if the axis cylinder itself were composed of transversely arranged 
bandlike or discoid masses (Frommann, Grandry). 

(3) The sheath of Schwann, a thin hyaline elastic membrane, surrounds the 
medullary cylinder. This outer sheath is possessed at regular intervals of annular 
constrictions, first discovered by Ranvier, and hence known as Ranvier's nodes. 
Each node is due to an annular fold of the sheath of Schwann projecting towards 
the axis cylinder. The part of the sheath between each two constrictions is called 
an ' interannular segment.' In the concavity of the constriction is a finely granular 
substance (Ranvier) of the nature of albuminous cement-substance. Corresponding 
to each constriction the medullary sheath is interrupted (Ranvier), so that the axis 
cylinder is here in contact with the sheath of Schwann. According to Engelmann also 
the axis cylinder is discontinuous at the node. The interruption of the medullary 
sheath at the nodes of Ranvier has probably an important bearing on the circula- 
tion of plasma to the axis cylinder (Ranvier). Owing to this state the nerve fibres 
present a peculiar dark cross at the node after silver staining, viz. the albuminous 
cement-substance around the constricting fold becomes stained by silver, and this 
penetrates hence gradually into the interior and stains a similar cement-substance 
covering the axis cylinder. According to whether the staining extends a longer or 
shorter distance on the surface of the axis cylinder upwards and downwards the node, 
the longitudinal branch of the 'cross/ appears longer or shorter (Axel Key and Retzius). 
The nodes of Ranvier are to be met with on all medullated nerve fibres of all verte- 
brates ; they are more numerous on broad nerve fibres than on thin ones (Axel Key 
and Retzius). 

(4) On the inner surface of the sheath of Schwann are elliptical nuclei surrounded 
by a smaller or larger film of protoplasm (Axel Key and Retzius, S. Mayer, and others). 
These nucleated cells do not belong to the sheath of Schwann, which, like the sarco- 
lemma, is structureless ; they are generally pressed against the medullary sheath, and are 
situated as it were in a small excavation of the outer surface of this latter structure. 
The protoplasm of these nucleated cells varies in amount in different states of 
development, and contains occasionally pigment granules (S. Meyer). The nuclei 
contain an intranuclear reticulum. Every interannular segment of the nerve fibres of 
higher vetebrates possesses as a rule only one such cell in about the middle of the 










p 
















MEDULLATED NERVE FIBRES. 87 

segment (Axel Key and Retzius), occasionally (though rarely) there are more than one 
(Lantermann). These cells, being analogous to the muscle corpuscles of striped muscle 
fibres, may be appropriately called nerve corpuscles. 

The medullated nerve fibres contained in the nerve bundles of a cerebro-spinal 
nerve trunk are of various thickness, as mentioned above, fine fibres being interspersed 
amongst thick ones ; in some nerve trunks, as the branches derived from the sacral 
plexus, the fine nerve fibres are in some bundles seen aggregated into special smaller or 
larger groups. 

Some medullated nerve fibres, especially motor fibres and the nerve fibres of 
electric organs, when approaching their terminal distribution, divide into two or more 
branches, the division taking place at a node of Ranvier. 

Some medullated nerve fibres, especially in the opticus and the central nervous 
organs, possess more or less regular varicose thickenings ; these are not due to a coagu- 
lation of the medullary sheath, as formerly believed, but to local accumulations, in the 
periaxial space, of the albuminous cement-substance mentioned above (Axel Key and 
Retzius). 

Medullated nerve fibres when approaching their terminal distribution lose their 
medullary sheath, they then consist merely of the axis cylinder and the sheath of Schwann, 
with the nucleated cells on its inner surface : these are the pale or non-medullated nerve 
fibres, to which we shall return in a future chapter. 

Still nearer the termination the non-medullated fibres lose their sheath of Schwann ; 
and now we have the axis cylinder merely covered from place to place with an elongated 
nucleated cell plate (Klein), generally of considerable size, and rolled more or less around 
the axis cylinder. This cell plate corresponds to a nerve corpuscle and possesses in some 
instances fine processes passing along the axis cylinder for a shorter or longer distance. 
Ultimately the axis cylinder becomes quite free, and separates into the constituent elemen- 
tary fibrils which become connected with each other into a network. (See a future chapter.) 

The elementary fibrils within the axis cylinder, and especially after they have 
separated from the latter, show, in the fresh condition as well as after staining with 
chloride of gold, minute more or less regular varicosities (Max Schultze, Cohnheim and 
others). 

PLATE XVII. 

Figures II. IV. and VI. after Axel Key and Retzius, ( Studien in der Anat. des 
Nervensystems/ Part II. Plate XVII. 



88 ATLAS OF HISTOLOGY. 

Fig. I. Part of a transverse section of sciatic nerve of dog, as seen under a magnify- 
ing power of about 40. 

Ep. Epineurium, consisting of bundles of connective-tissue fibres cut in different 
ways, and containing many vascular trunks cut transversely. 
F. Fat tissue contained in the epineurium. 

p. Perineurium, being the sheath for the individual nerve bundles. 
N. Nerve fibres, composing the nerve bundles cut transversely. 

Fig. II. Part of a transverse section of sciatic nerve of man ; magnifying power 
about 4. The lymphatics of the nerve have been injected with blue by 'puncture.' 
Numerous nerve bundles are shown surrounded by more or less continuous blue rings, 
the injected perineurium. 

Fig. I II. Transverse section through a microscopic nerve branch of human 
epiglottis ; magnifying power about 1 20. This branch represents a compound nerve 
bundle surrounded by perineurium. 

r. Perineurium, consisting of lamellae of fibrous-connective tissue, alternating with 
flattened nucleated connective-tissue cells. 

L. Lymph-space between perineurium and surface of nerve bundle. 
The medullated nerve fibres are seen as circles with a central dot, viz. medullary 
sheath and axis cylinder, in transverse section ; they are embedded in endoneurium, 
containing numerous nuclei, belonging to the connective-tissue cells of the latter. 

Fig. IV. Part of a transverse section of a nerve bundle of lumbar plexus of man. 
On the right are seen the lymph-spaces of the perineurium injected with blue matter ; 
they are in connection with similarly injected larger spaces (on the left) of the endoneu- 
rium, and with the minute spaces around the individual nerve fibres, seen in transverse 
sections. Magnifying power about 70. 

Fig. V. Transverse section through a nerve bundle of tail of mouse. Magnifying 
power about 1 20. 
p. Perineurium. 

l. Lymph-space of perineurium. 
E. Endoneurium. 

L. Lymph-spaces of endoneurium. 

Fig. VI. Part of a transverse section of sciatic nerve of man ; the lymph-spaces of 
the epineurium have been injected by 'puncture ' with blue matter. Magnifying power 
about 60. 





































& 









<fc 









STRUCTURE OF NERVE FIBRES. 



PLATE XVIII, 



89 



Figures IX. XI. and XIII. copied from Axel Key and Retzius, Part II. Plates 
VII. and VIII. 

Figures VII. and VIII. b drawn under a magnifying power of about 400; figures 
IX. XL and XIII. under one of about 750 ; and figures VIII. a, X. and XII. under 

about 300. 

Fig. VII. Medullated nerve fibres of sciatic nerve of frog, acted upon by chromate 
of ammonia. 

a. Showing in a surface view the reticular framework of the medullary sheath. 

B. The meshes are here much larger, owing probably to a swelling up of the fatty 
matter contained in the reticulum. 

c. Two nerve fibres, showing the deeply stained axis cylinder, the periaxial space, 
the medullary sheath, apparently composed of rods, and the fine sheath of Schwann. 
The left fibre shows a nucleus of the outer sheath, the right one shows a Ranvier's 
node ; the sheath of Schwann is incorrectly drawn, it ought to be constricted at the 
node. 

Fig. VIII. Two non-medullated nerve fibres of mesentery of newt, acted upon by 
chromate of ammonia, a, deeply stained with hematoxylin ; b, unstained. 

a shows an exceptionally broad wavy hyaline sheath of Schwann, surrounding the 
axis cylinder, which is here a small bundle of primitive fibrils. Two nuclei, show- 
ing the intranuclear network, belong to the nerve corpuscles of the sheath. 

b. A non-medullated nerve fibre that has left its sheath of Schwann, but is still 
covered with a very elongated cell-plate, nerve corpuscle, containing a long nucleus. 
This latter shows a beautiful reticulum. The cell-plate is in reality folded, and the axis 
cylinder, here a bundle of elementary fibrils, is fixed in the fold. 

Fig. IX. Part of a medullated nerve-fibre of brachial plexus of bird. The nerve 
had been prepared with perosmic acid ; it shows the medullary sheath composed oi 
shorter and longer imbricated sections, the hyaline sheath of Schwann, a nucleated nerve 
corpuscle between this and the medullary sheath, and pressed into a shallow excavation 
of the latter. 

Fig. X. Two nerve fibres of sciatic nerve of clog, after chromic acid and spirit; 
showing the axis cylinder, the nodes of Ranvier, the sheath of Schwann and nuclei, 
apparently belonging to this latter. There are traces of medullar)' substance to be seen 
as blotches inside the sheath of Schwann. 

v 



go ATLAS OF HISTOLOGY. 

Fig. XI. A node of Ranvier of a medullated nerve fibre, viewed from above. The 
medullary sheath is discontinuous at the node, whereas the axis cylinder passes from one 
segment into the other ; at the node the sheath of Schwann appears thickened. 

Fig. XII. Small dividing (sympathetic) bundle of medullated nerve fibres of mesen- 
tery, after acetic acid. The fine sheath covering the bundle and its branches, is the 
perineurium reduced to a single layer of nucleated endothelial plates seen in profile and 
at a short distance from the nerve fibres. These latter appear composed of longer or 
shorter sections. This appearance is entirely due to the medullary sheath of these fibres 
being composed of cylindrical sections, as described and figured above. The nuclei be- 
long to the nerve corpuscles of Schwann's sheath of the individual nerve fibres. 

Fig. XIII. Several fibres of.a bundle of medullated nerves, acted upon by nitrate of 
silver, of sparrow, to show the peculiar behaviour of the nodes of Ranvier towards this 
reagent. The silver has penetrated through the node and has stained the surface of the 
axis cylinder at this place for a short distance ; this forms the longitudinal branch of the 
'cross' mentioned on a former page. The axis cylinder and the outline of the medul- 
lary sheath are well seen in each fibre. 



Qi 



CHAPTER XIII. 

THE SPINAL CORD. 

The spinal cord is invested in a compound connective-tissue sheath, which is richly 
supplied with vessels and nerves, and is continued on to the nerve roots of the cord. 
This sheath is known as (a) Dura mater, (b) Arachnoidea, and (c) Pia mater. 

a) The dura mater is composed of lamellae more or less intimately connected with 
one another. In the outer part the lamellae possess a more circular, in the inner a more 
longitudinal course (Axel Key and Retzius). The number of lamellae varies of course 
according to the thickness of the dura ; each lamella consists of a layer of parallel 
bundles of fine connective-tissue fibres ; the bundles of neighbouring layers are placed 
under more or less acute angles. 

Between the lamellae lie flattened more or less branched connective-tissue cells 
arranged in a network. To these corpuscles corresponds, just as in the cornea (see 
p. 30), a system of lacunae and canals, the lymph-canalicular system. In some places a 
network of fine elastic fibres is present underneath the cell plates. 

The inner surface of the dura is covered with a thin hyaline elastic membrane, and 
on this is a continuous layer of nucleated endothelial plates, like that covering the serous 
membranes. The outer surface is also covered with a continuous layer of endothelium 
(Axel Key and Retzius). The dura mater is richly supplied with blood-vessels and nerves. 

b) The arachnoidea is, according to Axel Key and Retzius, a delicate membrane 
composed of paralled and closely placed bundles of connective-tissue fibres; between the 
bundles are the connective-tissue corpuscles. The bundles of this groundwork or 
' outer membrane ' have pre-eminently a longitudinal direction. On the outer free sur- 
face is an endothelial membrane composed of one or two layers of endothelial plates. On 
the inner surface lies a fenestrated membrane composed of anastomosing thinner and 
thicker trabeculae of connective-tissue fibres. The trabecule having chiefly a transverse 
direction, it follows that the meshes are stretched in a transverse diameter. This 
fenestrated or ' inner membrane ' is covered, on the surface directed towards the sub- 
arachnoidal space, by a single layer of endothelial plates. 

c) The pia mater consists (Axel Key and Retzius) of an external and an internal 
portion. The former is composed chiefly of longitudinal bundles of connective-tissue 
fibres, and is covered towards the subarachnoidal space with an endothelial membrane. 

Q 



92 ATLAS OF HISTOLOGY. 

The latter or intima pise is a meshwork of bundles of connective-tissue fibres ; its inner 
surface is lined with a layer of endotheloid cells, and between this layer and the connective- 
tissue meshwork is a network of fine elastic fibres. The numerous blood-vessels of the 
pia are situated between the external and internal layer, whence they penetrate, carried by 
a prolongation of the latter, into the substance of the cord. 

Numerous nerve fibres (medullated and non-medullated) may be traced (Axel Key 
and Retzius) in the external portion of the pia. They run either isolated or in small 
bundles, or they form a plexus. 

Between the arachnoidea and pia is a spongy tissue by which the subarachnoidal 
space becomes subdivided into numerous minute lacunae. This tissue is the sub- 
arachnoidal tissue, and it consists of a plexus of smaller and larger trabeculae of fibrous- 
connective tissue ensheathed in endothelium and containing a few elastic fibres. We 
have described and figured it on a former occasion as being identical with the fenestrated 
membrane composing the omentum. Axel Key and Retzius have shown that the 
subarachnoidal tissue is a prolongation of the inner or fenestrated portion of the arach- 
noidea. It forms in some places on the external surface of the pia, with which it is in 
continuity, smaller or larger membranous condensations as epipial tissue (Axel Key 
and Retzius). The trabeculae of the subarachnoidal tissue contain larger and smaller 
blood-vessels. 

On each side of the cord, from the foramen ovale magnum down to the filum 
terminale, between the anterior and posterior nerve roots, is the ligainentum denticulatum 
stretching like a diaphragm between arachnoidea and pia ; the subarachnoidal space is 
hereby subdivided into a spatium subarachnoidaleanterius and posterius (Axel Key and 
Retzius). 

The ligamentum denticulatum consists of trabeculae of connective-tissue bundles, 
anastomosing with one another and hereby forming a spongy or fenestrated substance ; 
the trabeculae are covered with endothelium. 

This tissue passes into the external layer of the pia mater. 



There are also isolated connective-tissue trabeculae extending between dura mater 
and arachnoidea ; they are ensheathed in endothelium, like all other structures, blood-vessels 
and nerves, passing from the one membrane to the other. These trabeculae are in some 
places more numerous than in others, most numerous in the posterior parts of the cord. 

Between the dura mater and arachnoidea is the subdural, between archnoidea and 
pia mater the subarachnoidal lymph space. The subdural space does not communi- 
cate with the subarachnoidal space (Luschka, Axel Key and Retzius). 



SHEATHS OF NERVE ROOTS. 

The nerve roots receive a prolongation from both the arachnoidea and dura mater as 
arachnoideal and dural sheath respectively (Axel Key and Retzius). And, in accord- 
ance with this, the lymph-spaces of the peripheral nerves (spinal as well as cerebral), 
and their ganglia, have been injected from the subdural and subarachnoidal spaces 
respectively (Axel Key and Retzius). 

Neither the subdural nor the subarachnoidal space is one open and free cavity, there 
being numerous connective-tissue trabecule passing between the dura mater and 
arachnoidea as well as between the latter and the pia mater (subarachnoidal tissue), 
as mentioned above. 



The cord itself contains a framework, and embedded in it the white and grey matter. 

A) The framework consists of the following parts : — 

i) A relatively large process of fibrous-connective tissue passes from the intima 
pias into the anterior fissure up to the anterior commissure, where it loses itself amongst 
the connective tissue of the white substance. 

Similar pial prolongations pass, at different points of the circumference, into the 
minute septa stretching between sections of the white matter, especially of the lateral 
and anterior tracts. 

All these prolongations of the intima pise carry blood-vessels into the cord. 

2) The chief part of the framework is a semifluid substance (neuroglia-matrix), 
which under certain reagents (chromates) presents a granular aspect (Gerlach), but 
in the fresh state and with other reagents is quite homogeneous (Walther). This 
substance fills all the interstices between the nervous elements of the cord. 

In this homogeneous matrix are embedded very numerous minute fibrils, neuroglia 
fibrils, which anastomose with one another in a network. These fibrils are in chemical 
respects similar to elastic fibrils (Gerlach), although they are not so resistent against 
acids and alkalies. 

In the white matter the neuroglia fibrils have pre-eminently a longitudinal direction^ 
except in the septulis, where they form networks in a transverse direction ; in the grey 
matter they extend uniformly in all directions. 

In connection with the network of neuroglia fibrils we find flattened branched 
nucleated connective-tissue corpuscles ; the processes of these lose themselves amongst 
the former. 

Neuroglia-matrix, neuroglia fibrils and branched cells form the ' Neuroglia.' These 

three substances have a definite relation to one another : the greater the amount of one, 

the greater is also that of the other two. 

Q 2 



94 ATLAS OF HISTOLOGY. 

The amount of neuroglia varies in different parts of the white and grey matter. 
It forms definite accumulations in the following parts : — 

a) On the external surface of the white matter it is present as a special peripheral 
crust underneath the intima pise ; the latter easily separates from the former. The 
neuroglia fibrils are pre-eminently horizontal. 

6) As septa passing between different sections of the white matter (posterior, 
lateral and anterior tracts). The so-called posterior fissure Is, properly speaking, only a 
septum of this kind. 

c) As the ground-substance of the anterior and posterior nerve roots from the point 
of entrance into the cord, 

d) A layer of neuroglia of considerable thickness surrounds the epithelium lining 
the central canal, as the ' central grey nucleus' of Kolliker. The neuroglia fibrils run 
here chiefly in three different directions : some are arranged in a circular manner, 
others longitudinally, and still others have a radiating direction. The first and second 
are most numerous ; the third are prolongations of the epithelial cells themselves, 
these being conical cells drawn out into a fine fibril passing radially into the 
depth. The basis of the epithelial cells is on the free surface and is covered with 
fine cilia. 

c) A peculiar accumulation of neuroglia is found in the posterior portion of the 
posterior horns of the grey matter as substantia gelatinosa of Rolando. 

Besides these accumulations of neuroglia there is a certain difference in the distri- 
bution of this substance in the various parts of the white matter, it being always more 
abundant in the inner and outer parts of the white matter, i.e. near the grey matter and 
the peripheral crust, than in the parts between. 

B) The white matter is composed of medullated nerve fibres. They vary in size, 
some being broad, others of medium size, and still others fine. Each nerve fibre 
possesses an axis cylinder, and around this a medullary sheath. The axis cylinder 
possesses the same fibrillar structure as that mentioned of the axis cylinder in general. In 
the broad fibres and in those of medium size the medullary sheath possesses a laminated 
structure. There is no definite evidence of the presence of a sheath of Swann or of 
nerve corpuscles, as in the medullated fibres of the cerebro-spinal nerves. The nerve 
fibres are embedded in, or separated by, neuroglia, as described above. The great bulk 
of the nerve fibres of the white matter run in a longitudinal direction, and are grouped 
as such, for each half of the cord, in the anterior, lateral and posterior tract. But the 
white matter contains also nerve fibres that have an oblique or even horizontal direction, 
Horizontal nerve fibres are present : — 



HORIZONTAL NERVE FIBRES OF CORD. 9S 

a) In the anterior commissure, i.e. at the bottom of the anterior fissure. The 
anterior commissure is composed merely of medullated nerve fibres that pass from the 
grey matter of the anterior horns of one side into the white matter of the anterior tract 
of the opposite side (Gerlach). 

6) Medullated nerve fibres emerge from the sides of the grey matter of the anterior 
horns, and after a short horizontal course enter the white matter of the lateral tracts. 

c) Similarly nerve fibres emerge from the grey matter of the posterior horns, and 
after a longer or shorter horizontal course enter the white matter of the posterior 
tracts (Gerlach). It is probable that they leave the posterior tracts again as the nerve 
fibres of the posterior nerve roots. 

d) The fibres of the posterior nerve roots pass into the grey matter of the posterior 
horns as horizontal fibres, either directly, as the lateral portion of the nerve roots, or 
indirectly, viz. by first entering the white matter of the posterior tract and running in 
it in a longitudinal direction upwards or downwards for a longer or shorter distance ; this 
is the median portion of the posterior nerve roots. 

The medullated nerve fibres of the anterior nerve roots pass in an oblique direction 
from the grey matter of the anterior horns through the white matter. 

The amount of white matter gradually increases towards the medulla oblongata. 

C) The grey matter occupies the central part of the cord in the well-known shape 
of an H, of which we distinguish the lateral parts or columns from the median part 
containing the central canal and the ( central grey nucleus ' of Kolliker surrounding it. 
Between this and the anterior fissure lies the anterior grey commissure, and in front of 
this the anterior white commissure ; behind the central grey nucleus lies the posterior 
commissure. The columns consist of an anterior, middle and posterior part, the former 
(viz. anterior) representing the anterior, the latter (viz. posterior) the posterior horn. 
The breadth and depth of the different parts of the grey matter vary in a definite 
manner in the different sections of the cord. 

The substance of each column of grey matter contains, in a matrix of neuroglia very 
similar in character to that of the white matter, (i) ganglion cells, and (2) nerve fibres. 

1) The ganglion cells are arranged more or less distinctly in groups. Thus they 
form three groups in the anterior horn : (a) an anterior, (b) a lateral, and (c) an inner 
group ; the ganglion cells of the lateral group are larger than those of the anterior, 
and these again larger than those of the inner group. 

In the dorsal region there is a group of large ganglion cells situated in the middle 
part of the column near the posterior commissure ; they represent Clarke's column 
(Lockhart Clarke), 



y6 ATLAS OF HISTOLOGY. 

The lateral group extends, in the cervical portion, into the white matter, i.e. in 
amongst the medullated nerve fibres. In the cervical swelling of the cord of calf the 
lateral group appears to be subdivided into an anterior group of large, and a posterior 
one of small spindle-shaped ganglion cells. 

In the posterior horns the ganglion cells are arranged as small groups in the anterior 
part, and as numerous isolated cells in the middle and lateral parts. The former are 
much larger than the latter, which are the smallest ganglion cells in the grey matter. 
A few small ganglion cells are present also around the 'central grey nucleus' 
(Gerlach). 

The ganglion cells are relatively large, branched cells, containing in some animals 
small masses of yellow pigment. Numerous minute fibrils can be distinguished in the 
cell substance (Max Schultze) ; these fibrils are connected with each other in a network. 
Each cell possesses in about the centre a large oval nucleus composed of a well-defined 
membrane, and containing an intranuclear network ; in about the middle of this is a large 
highly refractive thickening — nucleolus. Most ganglion cells, especially the large ones, 
are surrounded by a lymph-space, pericellular space, through which pass the processes 
of the cell. Their shape varies considerably, some cells being very elongated, others 
less so. But they are all possessed of several processes, i.e. they are multipolar. Some 
ganglion cells, especially those of the posterior horns, appear spindle-shaped, but each 
extremity is branched into several processes. 

Carriere found ganglion cells in the anterior horns anatomosing with one another 
by means of shorter or longer processes. 

The processes of the ganglion cells are of two kinds, branched and unbranched. 
The former are, just like the body of the ganglion cells, composed of fibrils, which 
run in a longitudinal direction and appear to pass in a fanlike manner from the pro- 
cesses into the body of the cell (Max Schultze). The branched processes ramify 
dichotomously into fine filaments. The unbranched processes are pale and finely 
striated bands, very attenuated where they join the cell-body; they represent the axis- 
cylinder processes discovered by Deiters. Gerlach has proved that they are present 
only in the ganglion cells of the anterior horns. The axis-cylinder process is generally 
single, occasionally there are two in one cell. After having left the cell-body the axis 
cylinder soon becomes ensheathed in a medullary sheath, that is, becomes converted 
into a medullated nerve fibre, which passes into an anterior nerve root. 

2) The nerve fibres of the grey matter are of different kinds : (a) the great bulk 
of the grey matter is composed of a minute and dense network of fine fibrils ; this 
has been first demonstrated by Gerlach. Deiters had already proved that the 
(medullated) nerve fibres which pass through the posterior nerve roots (either directly or 



RELATION OF GANGLION CELLS TO NERVE FIBRES. 97 

indirectly) into the grey matter undergo repeated division while in the latter, and 
Gerlach has shown that their ultimate branchlets anastomose with the above network. 
This network, which is known as Gerlach's nerve network, must therefore be regarded 
as composed of minute or primitive nerve fibrils. The nerve network surrounding the 
central grey nucleus of Kolliker is less dense than in other parts. 

Now, the branched processes of all ganglion cells of the grey matter attach 
themselves to Gerlach's nerve network, and there exists therefore an essential difference 
between the ganglion cells of the anterior and posterior horns (Gerlach) ; the former are 
connected, on the one hand, with Gerlach's nerve network, on the other hand they pass 
directly into a medullated nerve fibre of the anterior nerve root ; the latter are not 
directly connected with any nerve fibres, but anastomose with them only indirectly, 
viz. through Gerlach's nerve network. 

6) We have mentioned above that the axis-cylinder processes of the ganglion 
cells of the anterior horns pass through the latter as medullated nerve fibres, and 
enter the anterior nerve roots. But there are other nerve fibres that pass from 
the anterior nerve roots into the anterior horns without however belonging to 
any ganglion cells, viz. nerve fibres which enter the lateral tracts of the white 
matter, and pursue their course in this latter towards the brain as longitudinal fibres 
(Kolliker). 

c) Nerve fibres that originate in Gerlach's nerve network, chiefly of the outer 
portions of the grey matter, and having entered the lateral tracts of the white matter of 
the same side, pursue their course towards the brain as longitudinal nerve fibres. 

d) Similar fibres originating in Gerlach's nerve network of the anterior horns pass 
(through the anterior white commissure) into the anterior tracts of the white matter 
of the opposite side. 

e) Bundles of fine nerve fibres run horizontally from one column of the grey 
matter to the other, in front as anterior grey commissure, behind as posterior grey 
commissure. 

/) Numerous nerve fibres pass in a horizontal direction through the anterior 
portion of the posterior horns ; they branch very repeatedly (Gerlach). 

g) A large bundle of nerve fibres runs in a longitudinal direction and occupies 
about the middle of the posterior horns. This bundle receives fibres from the posterior 
tract of the white matter as well as from the posterior nerve root. 

h) In the dorsal region there exist bundles of fine nerve fibres which originate from 
Clarke's column of ganglion cells. These bundles, according to Gerlach, are three 
as a rule, viz. one running backwards, and two crossing each other, and passing in an 
outward direction. 



g8 ATLAS OF HISTOLOGY. 

i) The nerve fibres which enter the grey matter of the posterior horns as the 
lateral portion of the posterior nerve root have been mentioned above ; they run in 
this latter for a shorter or longer distance upwards or downwards in a longitudinal 
direction, and afterwards lose themselves in Gerlach's nerve network. 



The spinal cord is richly supplied with minute blood-vessels, each of which lies 
in a perivascular lymph-space formed by the neuroglia. 



99 



CHAPTER XIV. 

THE OPTIC NERVE. 

We shall consider in this chapter the optic nerve and its sheaths, up to near its passage 
through the cribrous membrane of the eyeball : this latter will be described in connection 
with the retina in a future chapter. 

i) The sheaths of the optic nerve. 

Through the investigations of Schwalbe, Axel Key and Retzius, H. Schmidt, 
Michel, Wolfring and Waldeyer, it is ascertained that the opticus possesses three dis- 
tinct sheaths : (a) An external sheath, being a prolongation of the dura mater (dural 
sheath, Axel Key and Retzius) ; it consists of fibrous-connective tissue of the same dense 
arrangement as in the dura mater of the brain and spinal cord, (b) A middle sheath 
(arachnoidal sheath, Axel Key and Retzius), being a continuation of the arachnoiclea ; 
it shows the same structure as this. (<r) An inner sheath of fibrous-connective tissue, 
being a continuation of the pia mater (pial sheath, Axel Key and Retzius). 

Between the dural and arachnoidal sheath is a continuous lymph space (subdural 
space of the optic nerve, Axel Key and Retzius ; subvaginal space, Schwalbe), in open 
communication with the subdural space of the brain. The surfaces of the dural and 
arachnoidal sheaths bordering on this space are covered with a single layer of endo- 
thelium. From the dural sheath pass a few connective-tissue trabecular through the 
subdural space to the arachnoidal sheath. 

Between the arachnoidal and pial sheath is another lymph space, the subarach- 
noidal space of the optic nerve (Axel Key and Retzius). This space is permeated by a 
spongy mass composed of anastomosing trabecular of connective tissue connected with 
the arachnoidal sheath, and identical in structure and arrangement with the subarachnoidal 
tissue mentioned in connection with the arachnoidea of the spinal cord. The surfaces 
of these trabecular, just like the surface of the arachnoidal and pial sheath bordering on 
the subarachnoidal space, are covered with an endothelial membrane. The subdural and 
subarachnoidal spaces of the optic do not intercommunicate with one another (Axel Key 
and Retzius), and can be freely injected separately from the subdural or subarachnoidal 
space respectively of the brain (Schwalbe, Axel Key and Retzius). 

2) The substance of the optic nerve proper. 

The optic nerve is composed of a great number of bundles of nerve fibres, sepa- 

R 



ioo ATLAS OF HISTOLOGY. 

rated by a framework of thicker and thinner trabecular of fibrous-connective tissue, 
with numerous connective-tissue cells, and directly continuous with the pial sheath of the 
optic nerve. This framework is, at the same time, the carrier of blood-vessels, large 
branches as well as capillary vessels. It forms a special accumulation around the 
arteria centralis. 

The bundles are of various sizes, some being two and three times thicker 
than others ; they are composed of medullated nerve fibres, that do not possess 
any sheath of Schwann. The medullary sheath appears sometimes to possess more or 
less regular varicosities, owing to an accumulation of fluid between axis cylinder and 
medullary sheath, as mentioned on a former occasion (p. 87). Under certain conditions 
(nitrate of silver), the nerve fibres do not show any such varicosities (Schwalbe). 

The individual nerve fibres within each bundle are separated from one another by a 
substance that, in all its essential characters, is identical with the neuroglia described of 
the white substance of the cord ; viz. (a) a hyaline, probably semifluid ground-sub- 
stance; (6) in this lies a network of fibrils, probably elastic, forming a network, and ar- 
ranged pre-eminently in a longitudinal direction ; and (c) numerous flat nucleated cells 
possessed of fine processes that lose themselves amongst the fibrils of the neuroglia. 

A large lymph-space may be injected (Axel Key and Retzius) on the inner surface 
of the pial sheath ; this space does not communicate with the subarachnoidal space of the 
optic nerve. It is continuous with lymph spaces situated between the bundles of nerve 
fibres and the trabeculae of the framework, and with smaller spaces within the trabecular. 
The perifascicular lymph spaces communicate with minute spaces separating the indi- 
vidual nerve fibres in a similar manner as described on p. 84, and figured on Plate XV 1 1. 
fig. IV. 

Besides the differences in structure between the optic nerve and spinal nerve, as 
described in a former chapter (XII.), there is this great distinction, that in an ordinary 
cerebro-spinal nerve the component bundles, nerve bundles, possess a special sheath, 
perineurium, as distinct from the general framework of the nerve, epineurium. But in the 
optic nerve this is not the case, the whole nerve being comparable to a compound nerve 
bundle (see p. 84, 6), the pial sheath being the perineurium, and the connective-tissue 
trabeculae in connection with it being the septa by which the subdivision into smaller 
and larger groups of nerve fibres is effected. 



PLATE XIX. 

Fig. I. Transverse section through the cervical part of the spinal cord of calf, one 
half of the cord being represented only. Magnifying power about 40. 




"0 • 



V 



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Ǥ 



/ 



Hi 



■*-m 



M^ 






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tfpn 



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STRUCTURE OF SPINAL CORD. 101 

w. White matter, showing the small septa passing into it from the periphery ; the 
nerve fibres (in transverse section) are represented only in the circumference of the grey 
matter. 

c. Central canal of grey matter. 
A. Anterior horn of grey matter. 

The processes that pass from the anterior and inner portion of the anterior horn, 
including the upper S, correspond to the anterior nerve roots. 

The process coming out from the posterior angle of the posterior horn, also marked 
S, corresponds to the lateral bundle of the posterior nerve root. 

In the grey matter the ganglion cells are indicated as larger or smaller corpuscles, each 
surrounded by a pericellular lymph space. The anterior and lateral group in the anterior 
horn are well shown ; also a few large cells in the front part of the posterior horn. 

Fig. II. The front part of the anterior horn of fig. I., more highly magnified. 
Numerous nerve fibres pass from the grey matter into the septa of the white matter ; 
this latter is not represented, except by a few adjacent medullated nerve fibres in trans- 
verse section. 

Fig. III. From a transverse section through the spinal cord of calf, magnified about 
1 80 diameters, showing part of the central canal, and the tissue immediately around it, 
viz. the ' central grey nucleus.' The canal is lined with epithelium, composed of 
ciliated more or less conical cells ; in most instances a filamentous process passes from the 
cell into the tissue underneath. This tissue contains, in a hyaline matrix, a network of 
fibrils ; most of these run horizontally, others have a longitudinal course, and appear 
therefore here cut transversly, i.e. as small dots. The nuclei correspond to the cells of 
the neuroglia, the cell substance not being shown. Both the nuclei of the neuroglia cells, 
as well as those of the epithelium, contain three or more large disc-shaped particles. But 
there is a delicate reticulum, besides, in the nucleus. This is, however, not seen on ac- 
count of the relatively low magnifying power. 

Fig. IV. Transverse section through the same cervical part of spinal cord of calf 
as represented in fig. I., seen under a lens. 
A. Anterior fissure. 

/. The tissue filling the so-called posterior fissure. 

Fig. V. Several multipolar ganglion cells, as they appear under a power of 100, in a 
section through the anterior horns of a hardened spinal cord. 

Fig. VI. Transverse section through the cervical swelling of the spinal cord of calf, 
as seen under a lens. The grey matter differs in its general outline from that of fig. IV., 
inasmuch as the anterior and posterior grey commissure is reduced to a thin plate. 



R 2 



ro2 ATLAS OF HISTOLOGY. 

Fig. VII. The posterior horn of grey matter shown in fig. I., under a higher mag- 
nifying power. 

;/. Nerve fibres, in transverse section, surrounding the grey matter. 
g. Large ganglion cells in the front part of the posterior horn ; there are several 
other small ones seen in the left part of the horn. Bundles of more or less horizontal 
nerve fibres are seen in the posterior and lateral portion ; they are fibres that pass 
either directly from the posterior nerve roots into the posterior horn, or that come 
from, or pass respectively into the posterior and lateral tract of the white matter. 

Fig. VIII. Portion of a transverse section through the grey matter (of cervical 
region) near the central canal. Magnifying power about 100. 

a. Nerve fibres, cut transversely, of anterior tract of white matter. The horizontal 
nerve fibres passing amongst them are the fibres forming the anterior commissure. 

b. Blood-vessels. 

c. Central canal. 

There are several large ganglion cells belonging to the front part of the posterior 
horn. 

Near the anterior tract of white substance (a) are a few small ganglion cells belong- 
ing to the inner group of cells of the anterior horn. 



PLATE XX. 

Fig. IX. From a transverse section through the white matter of the cord of calf 
(hardened in bichromate of potash). Magnifying power about 300. 

In the upper part are shown two isolated flattened nucleated branched cells of the 
neuroglia, under a somewhat higher power than the rest. In the bulk of the figure we 
see the nerve fibres in transverse section. They are of different sizes, and possess 
around the deeply stained axis cylinder a laminated medullary sheath. The nerve fibres 
are embedded in the neuroglia ; this contains in a matrix which is here granular, but 
under other conditions appears homogeneous, numerous elastic fibrils seen here in trans- 
verse sections as minute dots, on account of their having a course parallel to the long 
axis of the cord. Amongst the neuroglia are here seen two branched connective-tissue 
cells — neuroglia cells. 

Fig. X. Copied from Gerlach, part of ^g. 223, in Strickers' ' Handbook of His- 
tology.' A multipolar ganglion cell isolated from the grey matter of the cord, showing 
the numerous processes branching dichotomously, and losing themselves in the general 
network of fine nerve fibrils — Gerlach's nerve network. The minute dots amongst this 


















XIII 






i 















** 























STRUCTURE OF OPTIC NERVE. \o\ 

network are fibrils viewed in optical sections. In this network terminates a minute nerve, 
being a branch of a larger nerve that entered the grey matter. 

Fig. XL Small part of a transverse section of optic nerve. Magnifying power 
about 300. 

p. Pial or inner sheath, a fibrous-connective tissue, showing oblong nuclei of connec- 
tive-tissue corpuscles, and one or two blood-vessels in section. 

s. A septum passing from the inner sheath ; by such septa the nerve fibres are ar- 
ranged in groups ; in the present figure is shown part of a large group of nerve fibres. 
The nerve fibres are seen in transverse section, and each of them is indicated by a 
deeply stained small axis cylinder surrounded by a thin medullary sheath. The unequal 
size of the nerve fibres is probably due to their being possessed of varicosities, and 
therefore cut either through a varicosity or between. 

The nerve fibres are separated from the pial sheath by a large lymph space. Be- 
tween the fibres is seen neuroglia, composed like that of the cord of a general matrix, 
in which lies a network of elastic fibrils, and numerous branched flattened connective 
tissue cells. 

Fig. XII. From a transverse section through the most peripheral part of the white 
matter of the cord. Magnifying power about 300. 

w. White matter showing the transverse sections of the nerve fibres, separated by 
neuroglia, viz. hyaline matrix, network of neuroglia fibrils and numerous branched 
nucleated connective-tissue cells. 

c. Special peripheral layer of neuroglia on the surface of the white matter. The 
network of neuroglia fibrils has a pre-eminently horizontal direction. 

Fig. XIII. From a longitudinal section through a septum of the white matter of 
the cord, showing neuroglia fibrils and one branched neuroglia cell. Magnifying power 
about 450. 

Fig. XIV. From a transverse section through the white matter of a cord hardened 
in chromic acid. Nerve fibres of different sizes in transverse section; they show the 
medullary sheath greatly shrunk around the axis cylinder. The neuroglia, in its differ- 
ent parts, is well shown. Magnifying power about 450. 

Fig. XV. Copied from Gerlach, fig. 224 in Stackers' ' Handbook.' An isolated 
ganglion cell of the anterior horn of the human cord. Magnifying power 150. 

a. Axis-cylinder process. 

6. Pigment. 

The fine network in the upper part of the figure belongs to the nerve network of 
Gerlach, in which terminate the branched processes of the ganglion cell. 

Fig. XVI. Copied from Klein, fig. 7 1 in ' Handbook for the Physiological Labora- 



104 ATLAS OF HISTOLOGY. 

tory.' Isolated spindle-shaped ganglion cell of spinal cord of calf. Magnifying power 
about 450. 

Fig. XVII. From a transverse section through the cervical region of spinal cord of 
calf, showing six ganglion cells of the lateral group of the anterior horn extending 
between the nerve fibres of the white matter. Magnifying power about 350. 
G. Fibres of the grey matter passing into the lateral tracts. 
g. Ganglion cells. 

w. Medullated nerve fibres of the white matter in transverse section. 
The large nerve fibres with large axis cylinder are probably derived from the gan- 
glion cells, viz. axis-cylinder processes that have become invested in a medullary sheath. 
The ganglion cells extending chiefly in a longitudinal direction appear, in a trans- 
verse section, cut obliquely or transversely. 



i°5 



CHAPTER XV. 
THE BRAIN. 

The Membranes of the Brain. 

The description given of the minute structure of the membranes of the spinal cord 
applies also to those of the brain, with the following additions : — 

a) The blood-vessels of the dura mater cerebralis present a very peculiar arrange- 
ment and appearance (Boehm, Axel Key and Retzius, Paschkewicz, Michel) ; according 
to Axel Key and Retzius there is one system on the outer and another system on the 
inner surface. The former contains more or less wavy arteries accompanied on each side 
by a vein. The arteries branch dichotomously and anastomose with one another ; the 
same is the case with the veins. The inner system is a network of capillary vessels 
with elongated meshes. At the nodes of this network are peculiar ampullar, spindle- 
shaped or saccular dilatations. Now this inner system is connected with the outer one 
in two ways : first, by minute arterial branches (capillary arteries) passing in an oblique 
direction from the latter to the former, and, secondly, by the above ampulla; being con- 
nected by capillary veins with the veins of the outer system. So that these ampulla- 
represent the roots of the veins. 

b) The arachnoidal villi (Luschka), or glandular Pacchioni, are club-shaped or pear- 
shaped prolongations of the subarachnoidal network of trabecular of connective tissue 
(ensheathed in endothelium) ; they are covered by a thin continuation of the arachnoidea 
itself, including the covering endothelium (Axel Key and Retzius). These villi differ 
very much in size, some being single, others compound. They do not project into the 
subdural space, but are pushed with their stalks through minute holes of the inner 
laminar of the dura mater, and thus project into the venous sinuses of the latter; but 
they are not quite free in the sinus, being covered with a delicate membrane of connec- 
tive tissue and endothelium derived from the dura mater (Axel Key and Retzius). By 
injecting the subarachnoidal spaces of the brain Axel Key and Retzius found that the 
injection matter passes freely from the spongy subarachnoidal tissue through the stalks 
into the arachnoidal villi ; these being of the same spongy structure as the subarachnoidal 
tissue become, through the filling of their spaces, greatly enlarged ; then the injection 
matter fills the space between each villus and its dural covering, and finally enters the 



Io6 ATLAS OF HISTOLOGY. 

venous sinus itself. So that there exists a mediate connection between the subarach- 
noidal cavity and the venous sinuses of the brain. 

c) The pia cerebralis corresponds to the intima pise spinalis only. The numerous 
blood-vessels situated m the pia mater and passing to and from the brain possess a 
special outer sheath by means of which they are fixed on to the pia mater. When 
entering the brain-substance they carry with them that adventitial sheath (Kolliker, 
Virchow, Axel Key and Retzius, and others). This sheath is an endothelial membrane 
only in the capillary vessels, in the larger (arterial and venous) branches it contains in 
addition a variable amount of connective tissue. 

The telae choroideae are folds of the pia mater, including a prolongation of the 
subarachnoidal tissue. They possess on their free surface a layer of polyhedral endo- 
thelial cells, which in the embryo are ciliated. In man these cells are pigmented. 

The subdural space of the brain does not communicate with the subarachnoidal 
cavities nor with the ventricles (Luschka, Axel Key and Retzius). 

The subarachnoidal spaces do not communicate with a space said to exist between 
pia mater and brain substance proper (epicerebral space of His), the pia mater being 
everywhere in immediate contact with the brain surface. 

The Brain Substance. 

A) The framework or neuroglia of the grey and white matter of the brain (cerebrum, 
cerebellum and medulla oblongata) is very similar to that described of the spinal cord. 
It consists of (a) the same homogeneous (occasionally granular) matrix in which lie (d) 
numerous minute elastic fibrils connected into a network. In the white matter these 
fibrils possessing a pre-eminently longitudinal direction are parallel to the nerve fibres. 
(c) Branched nucleated flattened neuroglia cells — Deiters' cells — are connected with this 
network by their numerous processes (Boll, Golgi). 

Different from the spinal cord, the neuroglia of the white matter of the brain contains 
rows of small cells, each with a spherical nucleus, between bundles of nerve fibres. These 
small cells form special accumulations in the bulbus olfactorius and in the cerebellum. 
In the grey matter the numerous branched connective-tissue cells surrounding the 
blood-vessels (Boll) are specially to be mentioned. Lewis found them accumulated also 
around the ganglion cells of the cerebral hemispheres. According to Duke Charles of 
Bavaria, there are numerous colourless blood-corpuscles present around the blood- 
vessels and ganglion cells of the cerebral hemispheres, not only in disease, but also in 
the perfectly normal brain. 

The neuroglia forms a special accumulation lining the ventricles of the brain, the 
ependyma. This is a direct continuation of the ' central grey nucleus' of the cord, and 



WHITE MATTER OF BRAIN. Io; 

possesses the same structure. The epithelium lining the ventricles is likewise a layer of 
columnar ciliated epithelial cells. 

B) The white matter is distributed in the brain in the shape of large tracts of 
medullated nerve fibres, connecting the grey matter of different systems, collected in 
the roots of the cerebral nerves. These various tracts of nerve fibres in their special 
significance will be briefly mentioned presently. A detailed description of the dis- 
tribution of both, white and grey matter, will not be entered into here, since this 
is not so much a subject of Histology as of Anatomy. The reader will find in 
Stackers' ' Handbook' an exhaustive treatise by Meynert, the great authority on this 
subject. 

The nerve fibres of the white matter are, like those of the spinal cord, medullated, 
and without any sheath of Schwann. They vary greatly in size, some being broad, 
others of middle size, and many others very fine. They present themselves often in the 
shape of varicose fibres, that is : possessed of more or less regular swellings, which, as has 
been pointed out previously, are not due to a corresponding thickening of the medullary 
sheath, but to a local accumulation of fluid between this and the axis cylinder. Accord- 
ing to Boll there occur small multipolar ganglion cells between the nerve fibres of the 
white matter of the cerebral hemispheres. 

The white matter of the cerebral hemispheres is composed of the following masses 
of nerve fibres : (a) nerve fibres connecting the grey matter of the hemispheres with 
the large cerebral ganglia ; these fibres form the corona radiata, having a pre-eminently 
radiating direction, (b) There are masses of nerve fibres joining identical parts of the 
hemispheres of the two sides, as corpus callosum and anterior white commissure. 
(c) The association systems : these are fibres, more or less arcuate, on the inner surface 
of the cortex joining different parts of the hemispheres of the same side, (d) Special 
tracts of nerve fibres connecting the hemispheres with the cerebellum ; they branch off 
from the corona radiata, pass beneath the thalamus opticus and corpus quadrigeminum 
into the tegmentum cruris, and after a total crossing in the processus cerebelli ad 
corpus quadrigeminum enter the cerebellum. 

Meynert distinguishes the first section of the nervous conduction, viz. that between 
the grey matter of the cerebrum and the large cerebral ganglia, as the projection system 
of the first order. 

As projection system of the second order he considers the tracts of nerve fibres 
passing between the cerebral ganglia and the central grey matter lining the ventricles, 
viz. motor fibres passing through the crus cerebri and pons into the white matter 
of the cord. But the crus cerebri contains also sensory fibres ; these pass from the 



5 



ATLAS OF HISTOLOGY. 
108 

posterior tracts of the white natter of the cord through the pyramidal crossing into 
the crus and through this directly into the corona rad.ata. 

The projection system of the third order composes the tracts of nerve fibres 
belonging to the roots of the cerebral nerves. 

The white matter of the cerebellum, besides the above connect.on with the hem,- 
spheres, passes through the fasciculus cuneatus and gracilis (Burdach) into the posterior 
tract through the corpus restiforme into the lateral tract of the whtte matter of the 
spinal cord. Stilling s great work on the cerebellum gives a detailed account of the 
course of the fibres in that organ. 

C) The grey matter is distributed in the following four categories (Meynert) : 
(I) as the cortex of the cerebral hemispheres; (II) as the large cerebral ganglia, viz. 
corpus striatum, corpora albicantia, thalamus opticus and corpus quadrigeminum ; (III) 
as the grey substance of the medulla oblongata, rhomboidal fossa, and aqueductus 
Sylvii, the grey matter lining the ventricles, the tuber cinereum and infundibulum ; 
(IV) as the cortex and central grey matter of the cerebellum. 

In all parts of the grey matter we find, besides the neuroglia, a dense network of 
fine fibrils (Rindfleisch, Gerlach), directly connected with the terminal branches of 
repeatedly dividing fine medullated nerve fibres. 

This fine network corresponds completely to Gerlach's nerve network of the grey 

matter of the spinal cord. 

Embedded in the nerve network are ganglion cells, which vary as regards size, 
shape and arrangement in the different systems of the grey matter ; they are everywhere 
multipolar, and their processes lose themselves in the nerve network. Most of the 
ganglion cells possess however an unbranched axis-cylinder process that passes into 
the white matter, viz. becomes sooner or later invested in a medullary sheath, thus 
representing a medullated nerve fibre. 

1) Meynert distinguishes in the cortex of the cerebral hemispheres of man five 

layers : 

i) The superficial layer containing only few and small multipolar ganglion cells, 

the great bulk being occupied by neuroglia and the nerve network. 

2) The next layer possesses a large number of densely aggregated small ganglion 
cells of a more or less pyramidal shape. 

3) Then follows the chief layer, being the broadest and containing a large number 
of not particularly crowded pyramidal ganglion cells of large size. The pyramidal 
ganglion cells of these two layers are always placed vertically to the surface of the grey 



GANGLION CELLS OF GREY MATTER OF BRAIN 109 

matter : they possess, (a) a process of the apex more or less branched and directed 
towards the surface ; (£) the lateral processes of the basis, always branched ; both these 
processes lose themselves in the nerve network ; (y) the median process of the basis, 
being the axis-cylinder process, remains unbranched and passes downwards into the 
white matter as a medullated nerve fibre. 

4) This layer contains numerous small irregular ganglion cells with few branched 
processes ; while the ganglion cells of the former layers are regarded by Meynert as 
motor cells, the last-named ones are considered by him as connected with sensory nerves ; 
they represent the ' granular formation ' of Meynert 

5) The last layer contains more or less spindle-shaped and branched ganglion cells of 
medium size ; their direction is chiefly parallel to the surface. 

The processes of the ganglion cells of these different layers are, like those of the 
spinal cord, finely striated, being composed of minute fibrils. This is especially the case 
with those of the ganglion cells of the third or chief layer; Meynert, Huguenin and 
Boll describe also the axis cylinder of these cells as distinctly fibrillar. 

All these ganglion cells possess a spherical or slightly oval nucleus ; under some 
conditions of preparation this contains a large nucleolus. The cell substance is a distinct 
network of fibrils, and includes sometimes small masses of yellowish brown pigment. 

Each ganglion cell and its processes lie in a lymph space, pericellular space (Ober- 
steiner). 

Different from this arrangement, in five layers, is, according to Meynert: — 

a) The grey matter of the posterior portion of the occipital lobe about the sulcus 
hippocampi, in which Meynert distinguishes eight layers. The most prominent features 
are here the small multipolar cells, Meynert's ' granular formation.' 

6) The cortex of the cornu Ammonis, in which the small cells of the above fourth 
layer are wanting, but the cells of the second and especially of the third layer form the 
chief elements. Meynert on account of this designates the above third layer as the 
* formation of the cornu Ammonis.' 

c) In the walls of the fossa Sylvii, especially in the claustrum, the spindle-shaped 
cells of the above fourth layer are the prevalent features. 

d) The bulbus olfactorius. This contains a small central cavity lined with columnar 
ciliated cells, and a thick cortex. In man the upper part of this is white matter, being 
a continuation of the tract us olfactorius ; the rest is grey matter and consists, from below 
upwards, of: — 

a) A layer of non-medullated nerve fibres possessed of a sheath of Schwann ; these 
pass into the olfactory nerve proper, to the olfactory end-organ. 

3) Stratum glomerulosum. This consists of a layer of spherical or irregular glomeruli ; 



s 2 



IIO ATLAS OF HISTOLOGY. 

each glomerulus consists in man of a convolution of an olfactory nerve fibre, containing 
besides, numerous small nucleated Deiters* cells. 

y) Clarke's stratum gelatinosum, containing first small loose, then larger, denser 
multipolar ganglion cells of a spindle or pyramidal shape. Their processes lose them- 
selves in the fine nerve network forming the ground-substance for this layer. 

According to Golgi, the nerve fibres of the glomeruli undergo repeated division, 
and Huguenin saw in the dog processes of the ganglion cells of the third layer in con- 
nection with nerve fibres coming from the glomeruli. 

S) This layer is very thick and contains, in a network of fibrils, numerous smaller 
and larger groups of nuclei, similar in structure to the nuclear layer of the cerebellum 
(see below). 

II) In the large cerebral ganglia the cells are multipolar, and, as in the other regions, 
connected by their processes with the nerve network, which forms also here the matrix 
of the nervous part of the grey matter. In the thalamus opticus the ganglion cells are 
pre-eminently spindle-shaped (Meynert). 

In the corpus striatum the cells contain a large amount of pigment. 

III) The grey matter of this category represents chiefly the substance in which 
most of the cerebral nerves find their origin. The ganglion cells are multipolar and 
arranged in groups as the so-called ' nuclei ' of the respective nerves ; their processes, ex- 
cept the axis-cylinder process, terminate in the nerve network of the ground-substance. 

The cells of the different ' nuclei ' differ in size, aspect and number of processes. 
The cells of some regions, as some parts of the fossa rhomboidalis, or the substantia 
nigra Soemmeringi (between basis and tegmentum of the pedunculus cerebri), are filled 
with a dark brown pigment. 

The ganglion cells belonging to the ' nucleus ' of the optic nerve are multipolar and of 
different sizes. Meynert describes, in the anterior ganglion of the corpus quadri- 
geminum, large spindle-shaped cells belonging to a group of nerve fibres which join this 
ganglion with the ' nucleus ' of the oculomotor and trochlear nerve. 

The ganglion cells of these two nerves are situated underneath the aqueductus 
Sylvii ; they are large multipolar spindle-shaped cells, each with an axis-cylinder process. 

In the ' nuclei ' of the fifth are specially conspicuous the large multipolar ganglion 
cells, containing pigment ; they belong to its motor root situated in the anterior portion 
of the fossa rhomboidalis. The sensory nuclei contain small multipolar cells. 

Of a similar appearance are the ganglion cells representing the nucleus of the 
nervus abducens, situated laterally in the anterior part of the fossa rhomboidalis. 



GANGLION CELLS OF NERVE NUCLEI. in 

The ganglion cells of the ■ nucleus' of the facial nerve, in the depth of the fourth 
ventricle, are conspicuous by their size and their processes. 

The ganglion cells of the different portions of the ' nucleus' of the acoustic nerve 
are situated in the fossa rhomboidalis, near the surface, from the middle line to the 
pedunculi cerebelli ; they vary in size and shape ; those of the outer ' nucleus ' are 
fewer in number than those of the inner and anterior ( nucleus,' the former being at the 
same time pyramidal in shape. 

The cells of the ( nucleus ' of the glossopharyngeus and vagus, situated in the fossa 
rhomboidalis, are spindle-shaped. 

The ganglion cells of the spinal accessory nerve belong to the grey matter of the 
medulla oblongata behind the central canal ; they are large and multipolar. 

Conspicuous by their size are the multipolar ganglion cells representing the 
'nucleus' of the hypoglossal nerve, situated in front of the canal in the medulla 
oblongata. 

The olivary bodies contain in a matrix of grey nerve network slender multipolar 
ganglion cells. 

For a detailed account of the ' nuclei ' of the cerebral nerves the reader is referred 
to the works of Lockhart Clarke, Stilling, and Meynert. 

IV) The cortex of the cerebellum shows the following layers : — 
i) A broad cortical layer, the so-called molecular layer, containing in a ground- 
substance of nerve network (besides the neuroglia of the ordinary description) numerous 
dichotomously branched fibrillar processes ascending from the deeper layer (ganglion 
cells of Purkinje) and running towards the surface. On their way from the depth to 
the surface, the processes become finer and lose themselves partly in the nerve net- 
work, and partly in small pear-shaped multipolar ganglion cells (Sankey, Denissenko). 
The nerve network in the more superficial parts of this layer possesses an arrangement 
more or less distinctly vertical to the surface, except at this latter, where it is more 
horizontal. The nerve network of the deeper part is of an uniform arrangement. This 
superficial layer should be called more appropriately the fibrillar layer. 

2) A single layer of large spindle-shaped ganglion cells, Purkinje s cells. Each of 
them possesses one branched process extending into the former layer, and an unbranched 
or axis-cylinder process passing into the depth. The substance of each ganglion cell 
is a minute network of fibrils extending into the branched processes. The nucleus is 
spherical or oval. Each cell is surrounded by a pericellular space. Meynert ascribes 
to them a thin hyaline capsule ; according to Oberseiner this capsule is a network of 
neuroglia fibrils. 



II2 ATLAS OF HISTOLOGY. 

3) Between the layer of Purkinje's cells and the white matter is a broad layer, the 
nuclear layer. This contains a network of minute fibrils (Stieda, and Denissenko) 
continuous with, and similar in structure to, the nerve network of the cortex, and a great 
number of spherical nuclei, to which various investigators ascribe a totally different 
nature. "While some (Kolliker, Gerlach) regard them as belonging to neuroglia cells, 
others (Henle, Merkel) describe them as lymph corpuscles, and still others (Stilling) as 
minute multipolar ganglion cells. Denissenko distinguishes amongst them nuclei that 
belong to Deiters' or neuroglia cells, then nuclei that pertain to cells of a special 
nature, and nuclei indicative of small ganglion cells. 

The ' nuclei dentati ' of the cerebellum contain, just like the olivary bodies, a 
matrix of fine nerve network and slender multipolar ganglion cells. The 'nuclei* of 
Stilling, situated near the nuclei dentati, are distinguished from these latter by the 
greater size of their ganglion cells. 

The substance of the brain and cerebellum is rich in blood-vessels. Those of the 
grey matter pass from the pia (or vice versa) in a more or less vertical and oblique 
direction and anastomose into an uniform network. Those of the white matter form a 
network, the meshes of which are pre-eminently longitudinal. The vessels lie in- 
vaginated in lymph channels, perivascular lymphatics of His. Between the vascular 
adventitia and the neuroglia boundary of the perivascular channel extend numerous 
neuroglia fibrils. The pericellular lymph spaces, mentioned above as surrounding the 
ganglion cells and their processes, anastomose with the perivascular lymph channels 
(Lewis). 

The hypophysis cerebri and the pineal gland will be considered in a future chapter, 
in connection with several other organs, as the suprarenal capsule and coccygeal gland, 
whose structure and function are not well known. 



PLATE XXI. 

Fig. I. Vertical section through the grey matter of the cerebral hemisphere of dog, 
as seen under a low power. On the left side is the superficial layer of the cortical grey 
matter. Owing to the low power the small ganglion cells and the neuroglia cells in it 
are not visible. A blood-vessel is seen passing from the surface into this layer. Next 
follows a layer of small ganglion cells, then a broad layer of ganglion cells, gradually 
increasing in size — ■ formation of the cornu Ammonis,' Meynert. The ' granular forma- 
tion ' of small cells, viz. the fourth layer in the human cortex, and the fifth layer of 
spindle-shaped cells, is not visible here. 

The ganglion cells in this and the next following figure are in so far of a peculiar 



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DIFFERENT LAYERS IN THE CORTEX OF CEREBELLUM. n 3 

aspect, as the space is well shown in which lie cell and processes, especially the process 
of the apex ; the substance of the ganglion cells is not visible except the nucleus and 
its nucleolus. 

Fig. II. From the same section as fig. L, more highly magnified. The matrix is a net- 
work of minutefibrils, possessing chieflyadirection vertical to the surface of the hemisphere. 

The ganglion cells are marked by their pericellular space ; of the substance of the 
cells only the nucleus and its nucleolus are visible. Several deeply stained nuclei belong- 
ing to the neuroglia cells, or cells of Deiters, are contained in the matrix. 

A branched capillary vessel with its perivascular space is seen in the right lower part 
of the figure. 

Figures III. IV. and V. show isolated, chiefly pyramidal, ganglion cells of various 
sizes, of the grey matter of the cerebral hemispheres of man. Fig. IV. shows the typical 
pyramidal cells of the ' formation of the cornu Ammonis ; ' they possess a long process 
of the apex, terminating in the fine nerve network of the cortex, so do also the lateral 
basilar processes. The median basilar process is, in most instances, the unbranched axis- 
cylinder process, but in this instance it appears branched. 

Fig. VI. Vertical section through the grey matterof the human cerebellum Magni- 
fying power about ioo. 

a. The superficial, so-called molecular, or better fibrillar layer, containing in a matrix 
of fine nerve networks the dichotomously branched processes of the large ganglion cells 
of Purkinje, that form the second layer b. 

The nuclei of the fibrillar layer belong partly to small ganglion cells, partly to 
Deiters' neuroglia cells. Two (branched) capillary blood-vessels pass from the free surface, 
that is, from the pia mater, into the grey matter. 

c. Nuclear layer, containing, in a fine nerve network, numerous groups of nucleated 
cells, of which only the nuclei are visible. 

d. Part of white substance. 

Fig. VII. Vertical section through a 'lamina' of cerebellum of rat, showing the 
distribution of the blood-vessels, injected with carmine gelatine, seen under a low magni- 
fying power. 

a. Pia mater of the surface. 

6. Fibrillar cortex, so-called molecular layer. 

c. Nuclear layer. Between this and the preceding layer are indications of Purkinje s 

cells. 

d. White matter forming the centre of the 'lamina.' The capillary blood- 
vessels of the grey matter are more numerous than those of the white matter ; in the 
cortical layer the vessels have a more or less vertical direction. 



H4 ATLAS OF HISTOLOGY. 



CHAPTER XVI. 

CEREBROSPINAL GANGLIA. 

It has been mentioned in a former chapter that the spinal nerves, when leaving the 
cord, receive from both the dura mater and arachnoidea a special investing sheath viz 
the dural and arachnoidal sheath. The pia mater does not send any prolongation on 
to the nerves, but is merely perforated by them. The same holds good for the 
cerebral nerves. 

The dural sheath of the ordinary cerebrospinal nerves becomes identified with 
the epineurium, the arachnoidal sheath with the perineurium described in Chapter XII 
p. 84. 

The cerebro-spinal ganglia possess a continuation of both the dural and arach- 
noidal sheath (Axel Key and Retzius), the former being placed quite peripherally the 
latter more internally. The former is, like the epineurium of nerve trunks, to which 
it corresponds, composed of more or less dense fibrous-connective tissue, connective- 
tissue corpuscles, and networks of elastic fibres ; the latter possesses, just like the 
perineurium of the nerve bundles, a lamellar structure, thin lamella of bundles of 
fibrous-connective tissue alternating with flattened endotheloid connective-tissue cor- 
puscles. 

Both the epineural and perineural connective tissue of the ganglia send into the 
nterior longer or shorter septa. Those of the latter (viz. perineurium) follow the larger 
and smaller nerve bundles that permeate each ganglion in different directions. 

The endoneurium of the nerve-roots passes also into the ganglion between groups 
and individual ganglion cells, as the so-called interstitial tissue. Its structure is similar 
to that of the nerve bundles, being a homogeneous matrix containing in some places 
minute bundles of connective-tissue fibrils ; protoplasmic nucleated cells are also 
present in it. These are very numerous, and in all their characters are identical with 
the flattened connective-tissue cells described of the endoneurium of the nerve 
bundles. 

The endoneural connective tissue of the ganglion contains numerous capillary 
blood-vessels connected into a network, and nerve fibres that wind themselves through 
the groups of ganglion cells. 



CEREBROSPINAL GANGLIA. „j 

Following the nerve trunk into the ganglion, we notice that the ganglion cells 
form at first smaller or larger groups or rows between the peripheral nerve bundl* , 
by-and-bye they appear also between the central ones ; finally their number increases 
to such an extent that the nerve bundles become split up into small groups of fibres 
winch run between the groups of ganglion cells in an oblique or longitudinal, or even 
transverse direction. 

The nerve fibres in the cerebrospinal ganglia of man and other vertebrates are 
as a rule, medullated nerve fibres of the same structure as those described of the 
cerebrospinal nerves; amongst them we meet also with a few non-medullatcd nerve 
fibres, i.e. axis cylinder with hyaline sheath of Schwann and nerve corpuscles. 

The ganglion cells themselves are spherical, oval, or pear-shaped cells, occasionally 
slightly flattened. They vary considerably in size, some being three and four times as 
large as others. Their substance contains a homogeneous interstitial matrix, and a fine 
network of fibrils (Schwalbe), which occasionally near the periphery possess an arrange- 
ment parallel to the surface, and therefore are more or less concentric. Each ganglion 
cell contains about the centre a relatively large well-defined spherical or slightly oval 
nucleus, which under certain conditions shows an intranuclear network. In & many in- 
stances it contains one large nucleolus, seldom two such nucleoli. Generally each gan- 
glion-cell possesses a larger or smaller clump of yellowish pigment granules. 

Most ganglion cells are possessed of one process, unipolar cells (Kolliker, Lieber- 
kiihn, Fraentzel, Courvoisier, Schwalbe, Stieda, and others). This process is a direct 
prolongation of the fibrillar network of the substance of the cell, and appears therefore 
finely and longitudinally striated (Max Schultse, Schwalbe, Key and Retzius). This 
process is directly continuous with the axis cylinder of a nerve fibre, and may there- 
fore be called the axis-cylinder process. The smaller examples of the ganglion cells 
appear to be without any such process, that is, they are apolar (Kolliker, Key and 
Retzius) ; such ganglion cells are probably young or embryonal forms. 

Each ganglion cell is enclosed in a special capsule. This is a homogeneous thin 
hyaline membrane, identical with the hyaline sheath of Schwann of nerve fibres. Inside 
this hyaline capsule lies a layer of small, more or less polyhedral or flattened proto- 
plasmic cells, each with a round or slightly oval nucleus ; they represent in some 
instances an almost complete epitheloid lining. 

The capsule and its lining cells have been known through the observations of many 

authors (Henle, Robin, Axmann, Leydig, Kolliker, Courvoisier, Stieda, and others). 

1 he number of these lining corpuscles varies in different ganglia and in different ganglion 

cells of the same ganglion; they are generally most numerous near the axis-cylinder 

process (Arndt). 



T 



u6 ATLAS OF HISTOLOGY. 

The ganglion cell in the fresh and unaltered state generally completely fills the 
space of its capsule, so that its surface is almost in immediate contact with the 
above cell-lining of the capsule (Key and Retzius, MacCarthy). After shrinking, the 
ganglion cell withdraws from the capsule to a greater or lesser extent ; hereby the 
ganglion cell draws away part of the substance of the capsular cells, and appears then 
as if possessed of many processes (Key and Retzius). Max Schultze, Arndt, and 
others have misinterpreted these processes for nerve processes. 

The axis-cylinder process of the ganglion cells of the cerebro-spinal ganglia of 
man and mammals, occasionally still within the capsule, but generally after having 
left the cell, becomes twisted and convoluted, sometimes in a very complex manner 
(glomerulus of Key and Retzius), but sooner or later it is ensheathed in a medul- 
lary sheath of the same structure as in ordinary nerves. Outside this is a hyaline 
sheath of Schwann, being the direct continuation of the hyaline capsule of the ganglion 
cell. The medullated nerve fibre is now complete even to the nodes of Ranvier, and the 
nerve corpuscles, viz. the isolated nucleated cells placed at intervals on the inner side of 
the sheath of Schwann. 

The nerve corpuscles are the direct continuations of the cells lining the capsule 
of the ganglion cells. 

In the ganglion cells of rabbit Ranvier has pointed out an interesting relation to 
exist, viz. that at a certain distance from the ganglion cell, the axis-cylinder process 
becomes thicker and converted into a medullated nerve fibre, and that this latter 
shows a T-shaped division, taking place generally at the first node of Ranvier. Key 
and Retzius confirmed this, but met it only in a limited number of nerve fibres, and 
are therefore disinclined to ascribe to it a character of general importance. 

In a few cases the axis-cylinder process does not obtain a medullary sheath, but 
only the hyaline sheath of Schwann, and is therefore converted into a non-medullated 
nerve fibre. 

The ganglion cells of the cerebro-spinal ganglia of amphibian animals and fishes differ 
in no essential point from those of mammals. 

Next to the ganglia proper of fishes, there are in the nerve trunks isolated ganglion 
cells differing in many respects from the ordinary cerebro-spinal ganglion cells. These 
cells are bipolar, possessing at each pole an axis-cylinder process (Bidder, Volkmann, 
Max Schultze, and others), which is continuous with the axis cylinder of a medullated 
nerve fibre. On the inside of the capsule of the cell there are only a few nucleated cells. 
The ganglion cells of the cerebro-spinal ganglia of petromyzon Planeri are, 
according to Langerhans, Stannius, Key and Retzius, bipolar; one axis-cylinder process 
is directed towards the periphery, and is broader than the other, which is directed towards 



LYMPH-SPACES OF GANGLIA.; II? 

the brain (Stannius, Langerhans) : both become invested in a hyaline sheath of Schwann 
which is a continuation of the capsule of the ganglion cell ; but they remain without a 
medullary sheath and represent therefore non-medullated nerve fibres. The capsule 
of the ganglion cell is a hyaline delicate membrane, lined with a special layer of nucleated 
cells, just as in the spinal ganglia of higher animals. 

Key and Retzius injected from the subdural and subarachnoidal spaces of the 
cord the corresponding spaces of the nerve roots and of the ganglia. The lamellar septa 
of the ganglia, viz. those continuous with the perineurium of the nerve bundles, contain 
also lymph spaces which, on the one hand, are connected with the subarachnoidal spaces 
of the ganglion, and, on the other, pass into the very dense network of channels and 
spaces in the endoneural ganglionic connective tissue. The ganglion cells, just like the 
nerve fibres of the cerebro-spinal nerves mentioned in Chapter XII., are surrounded by 
these channels and spaces. 



T i 



Il8 ATLAS OF HISTOLOGY. 



CHAPTER XVII. 

THE SYMPATHETIC SYSTEM. 

A. The Sympathetic Nerve Fibres. 

The sympathetic nerve trunks resemble those of the cerebro-spinal system ; they contain 
medullated and non-medullated nerve fibres. Unlike the cerebro-spinal system, the 
former are in some parts less numerous than the latter. 

The medullated nerve fibres of the sympathetic vary in breadth ; they decrease in 
number towards the periphery. As regards structure, they in no way differ from the 
medullated nerve fibres of the cerebro-spinal nerves, viz. they possess : (a) an axis 
cylinder finely striated, being composed of fine fibrils, elementary nerve fibrils; 
(6) a medullary sheath ; (c) a hyaline sheath of Schwann ; and on the inside of 
this (d) nucleated nerve corpuscles. They show also Ranvier's nodes. The medullated 
nerve fibres of medium size, and also the fine ones, show occasionally more or less 

regular varicosities. 

The non-medullated nerve fibres, or Remak's fibres, are pale, finely fibrillar axis 
cylinders, many of them invested in a hyaline sheath of Schwann with nerve corpuscles 
(Remak, Max Schultze, Waldeyer) ; that is to say, they completely resemble the non- 
medullated nerve fibres of the cerebro-spinal nerves described in a former chapter. 
They branch very often into two or three fine fibres. There are, however, some fine 
axis cylinders which do not appear to possess any sheath of Schwann, but only a few 
nerve corpuscles. They are to be met with in numbers at the peripheral distribution of 

the sympathetic nerves. 

The number of non-medullated nerve fibres is always considerable in the trunks 
and increases towards the periphery, so that the peripheral nerve branches possess many 
more non-medullated than medullated fibres. 

The microscopic branches, bundles, of the sympathetic system are invested in a 
thin perineurium, which in the small examples is merely an endothelial membrane; in 
the larger ones it contains also a small amount of fibrous-connective tissue. 



SYMPATHETIC GANGLIA. 119 

B. The Sympathetic Ganglia. 

The large sympathetic gangia are, as regards the arrangement of their connective- 
tissue sheaths and lymph-paths, identical with the cerebro-spinal ganglia described in the 
previous chapter (Key and Retzius). The sympathetic system contains, however, very 
numerous microscopic ganglia in connection with minute nerve branches, such as occur 
in the different parts of the alimentary canal, the uro-genital organs, carotic plexus, 
cardiac nerves, &c. These microscopic ganglia represent spherical or elliptical or irregu- 
larly shaped accumulations of ganglion cells at the point of anastomosis of two, three, or 
more minute nerve branches ; occasionally they form a lateral budlike or spindle-shaped 
swelling in the course of one nerve branch. They vary very greatly in size, from one 
or two ganglion cells placed between the fibres of a minute nerve branch, to longer or 
shorter chains or clumps of ganglion cells. 

The nerve branches that are connected with these microscopic ganglia possess a 
delicate sheath, a simple layer of endothelium, and contain in the majority of instances 
only non-medullated nerve fibres of various thicknesses. Where the ganglion represents 
a clump of cells placed at the point of anastomosis of nerve branches, we notice that the 
endothelial sheath of the latter is continued also over the ganglion. 

The ganglion cells of the sympathetic system are of very various sizes and shapes. 
Asa rule, they are smaller than the cells of the cerebro-spinal ganglia ; they are elliptical, 
spherical, club-shaped or pear-shaped. They possess a hyaline capsule lined by flattened 
nucleated cells (Henle, Hannover, Kollmann, Arnstein, Fraentzel, Max Schultze, Stieda, 
and others). If the cell-substance withdraws (through shrinking or otherwise) from 
the capsule, it very often remains connected by fine processes with the nucleated cells 
lining the capsule (Key and Retzius), similar to what has been described above of 
the ganglion cells of the cerebro-spinal ganglia. Occasionally there are more than one 
cell in a common capsule (Courvoisier, S. Mayer). 

The substance of the sympathetic ganglion cells is in some instances a distinct net- 
work of fibrils, in others it appears coarsely granular. It contains in some instances a 
clump of pigment granules. As a rule there is one excentric large, spherical or oval 
nucleus; occasionally (especially in the rabbit, Remak) the nucleus is double. It pos- 
sesses a limiting membrane, a more or less distinct intranuclear network, and in this 
often a large nucleolus. 

The ganglion cells are apolar, unipolar, bipolar and multipolar. 

The apolar cells are generally comparatively small cells, forming groups or nests 
(S. Mayer, Lavdowsky) ; they occur especially in batrachian animals, and represent 
embryonal forms. 



120 ATLAS OF HISTOLOGY. 

The unipolar cells are found in almost all sympathetic ganglia. They are met with 
especially in the microscopic ganglia of the alimentary canal and genital organs of 
mammals. They possess a finely striated axis-cylinder process, which, as in other 
instances, is a continuation of the cell substance, and carries with it a prolongation 
of the capsule of the cell, as sheath of Schwann, and of the nucleated cells as nerve 
corpuscles. 

The bipolar cells are similar to the former, except that they possess two processes, 
one at each pole — the cell appears thus spindle-shaped — or they are both coming off 
from one side of the cell either close together or somewhat apart from one another. 

The multipolar cells are very common in man and other mammals (Kollmann, 
Arnstein, Schwalbe, and others), especially in the larger sympathetic ganglia. Their 
processes vary from 3 to 5 or more, they are of very various thickness; some are 
branched, others unbranched. 

In all instances, no matter whether uni- bi- or multipolar, each process is a continu- 
ation of the cell-substance, and obtains a prolongation from the hyaline capsule of the 
cell as the hyaline sheath of Schwann, and of the lining capsular cells, as the nerve 
corpuscles, that is to say it becomes converted into a non-medullated nerve fibre. 

In frog the ganglion cells, especially the bipolar ones, are of a peculiar nature, inas- 
much as one of their processes appears as a 'spiral fibre ' twisted round the other 
process, 'the straight fibre.' These cells have been discovered by Beale, and are 
known as Beale's ganglion cells with spiral fibre. The spiral fibre is generally thinner 
than the straight fibre, and where it leaves the cell-substance there exists always an 
accumulation of small nuclei. The spiral fibre is in some instances branched, and the 
branches anastomose into a network (Arnold, Kolliker, Courvoisier). The spiral fibre, 
at first thin, becomes soon thicker and transformed into a medullated nerve fibre, 
whereas the straight one remains non-medullated (Hoffmann, especially Key and 
Retzius). 

The spiral fibre is at first enclosed in a common sheath with the straight one, but 
sooner or later leaves this latter in its own sheath of Schwann. 

Similar cells, viz. with 'spiral fibre,' but less distinct than in the frog, are met with 
in mammals (Courvoisier, Bidder, Klein). 

The special character and distribution of the sympathetic ganglia of the alimentary 
canal, and uro-genital organs, will be mentioned in connection with the description of 
these organs in future chapters. 



' 



xxn. 








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Miniorn Bj.o« wijj 



CEREBROSPINAL GANGLION CELLS. iai 



PLATE XXII. 

Figs. I. and III. are copied from Key and Retzius. 

Fig. I. An isolated ganglion cell of a spinal ganglion of toad. Magnifying power 
about 570. 

The large cell with its nucleus and nucleolus, the capsule, the axis-cylinder process 
becoming invested in a medullary sheath, and the continuation of the sheath of Schwann 
with the cell capsule, are well shown. 

Fig. II. From a section through a microscopic ganglion of the submaxillary gland 
of dog. Magnifying power about 300. 

c. Capsule of the ganglion. 

n. Nerve fibres passing out of the ganglion ; the nerve fibres entering the ganglion 
are not contained in the section, they are connected with the upper right portion. The 
nerve fibres are ordinary medullated fibres, the details of their structure are not 
represented, owing to the low magnifying power. The ganglion cells are invested in a 
special capsule, lined by a few nuclei, here represented as if contained in the capsule. 

Fig. III. A large and small ganglion cell of the ganglion Gasseri of rabbit. The 
axis cylinder immediately after leaving the cell is much convoluted, it becomes trans- 
formed into a medullated nerve fibre, which at a certain distance shows a T-shaped 
division of Ranvier. 

The structure of the nerve fibre is the same as represented in fig. IX. of Plate 
XVIII. Magnifying power 850. 

Fig. IV. A microscopic ganglion of the sympathetic of the bladder of rabbit. 
Magnifying power about 250. 

b. Nerve branches, composed of non-medullated fibres, not shown in detail. 

g. Ganglion cells ; the ganglion is a group of ganglion cells situated at the point of 
anastomosis of several nerve branches. 

Fig. V. From the plexus of Meissner of the small intestine, prepared with chloride 
of gold, of toad ; it represents a plexus of broader and narrower axis cylinders composed 
of elementary nerve fibrils. These fibrils are beaded, and they appear such in all 
preparations prepared with chloride of gold. There are several small and large single 
ganglion cells (6) apparently unipolar, each with a clear nucleus, and connected with 
the branches of the plexus. In the enlarged parts (a) of the plexus are groups of multi- 
polar ganglion cells of various sizes, each with a clear nucleus. Magnifying power 
about 150. 



122 ATLAS OF HISTOLOGY. 

Fig. VI. Copied from MacCarthy ; a ganglion cell of a spinal ganglion, to show 

a. the capsule ; 

A the nucleated cells lining the capsule, their outline is not well marked ; 

c. the substance of the ganglion cell ; 
n. nucleus ; 

d. clump of pigment granules. 

The process of the ganglion cell is not represented. 

Fig. VII. Copied from Klein, Plate XXXVII., 'Handbook for the Physiol. 
Laboratory/ Magnifying power about 350. 

From a section through the tongue, stained with chloride of gold, of frog. 
A. minute artery ; 

a. capillaries ; 

b, plasma cells of the intermuscular tissue ; 

c. non-medullated nerve fibres; 

d, fine non-medullated nerve fibres forming a plexus, they possess nuclei indicative 
of nerve corpuscles. 

PLATE XXIII. 

Figs. VIII. and X. copied from Key and Retzius. 

Fig. VIII. An isolated sympathetic ganglion cell of man; it shows: the capsule 
lined with nucleated cells ; the nucleus of the ganglion cell with a large nucleolus ; three 
unbranched and one branched process. The cell capsule is continued over all processes 
as the sheath of Schwann. Magnifying power 750. 

Fig. IX. A small group of ganglion cells connected with a sympathetic nerve 
branch of bladder of dog (chloride of gold). 

The ganglion cells possess each a capsule, the nuclei lining this are represented as 
if hi it. In three cells the process is shown that is continuous with the axis cylinder of 
a non-medullated nerve fibre. On the right is a large ganglion cell as if dividing. 

The detail of structure of the nerve fibres is not shown ; the sheath of the nerve 
branch is continuous over the ganglion. Magnifying power about 350. 

Fig. X. Isolated sympathetic ganglion cell of frog, showing the 'spiral fibre' of 
Beale. This spiral fibre is continuous with the axis cylinder of a medullated nerve 
fibre, while the 'straight process' remains without a medullary sheath. Magnifying 
power 1,100. 

Figs. XI. and XII. copied from Klein, Plate XXVI., ' Handbook for the Physiol. 
Laboratory.' 



ATI. 



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1st 



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XII 









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I ■ 



GANGLION CELLS WITH SPIRAL FIBRE, 123 

Fig. XI. Three ganglion cells with 'spiral fibre' in a sympathetic nerve branch 
of the muscular coat of the bladder of rabbit. Magnifying power about 500. 

Only the axis cylinders coming off from the ganglion cells are drawn here ; the 
other nerve fibres are left in outline, except the sheath with its nuclei. 

Fig. XII. From a similar preparation as the preceding figure, showing seven 
ganglion cells embedded amongst the non-medullated nerve fibres. The upper part 
of the nerve branch divides into two. Magnifying power about 300. 

Fig. XIII. Two sympathetic nerve fibres (man) embedded in a thick fibrous 
sheath of Henle. 

Each nerve fibre possesses a medullary sheath only from place to place ; this gives 
it the appearance of a varicose fibre. Magnifying power about 350. 

Fig. XIV. Several nerve fibres of a sympathetic branch of rabbit. 

Three are non-medullated and of various sizes; the broad fibre divides into two. 

One is a fine medullated fibre. 

The nuclei are indicative of the nerve corpuscles lining the sheath of Schwann. 
Magnifying power about 350. 

Fig. XV. A sympathetic nerve branch of mesentery of cat, after nitrate of silver. 
Its sheath is an endothelial membrane ; only the outlines of the endothelial cells are here 
represented. Magnifying power about 150. 



u 



I24 ATLAS OF HISTOLOGY. 



CHAPTER XVIII. 

PERIPHERAL DISTRIBUTION OF NERVES. 

As has been mentioned on a former occasion, the nerve bundles, ensheathed in their 
perineurium, represent the microscopic nerve branches. By repeated division the 
number of nerve fibres composing a branch becomes gradually reduced. All the fine 
branches of a nerve bundle down to those that contain only one or two nerve fibres 
possess a sheath which is a continuation of die perineurium. This sheath varies in its 
thickness in different localities, in some places it is merely an endothelial membrane, in 
others it is of considerable thickness and consists then of fibrous-connective tissue and 
endotheloid cells. This sheath is called Henle's sheath, or also perineurial sheath (Key 

and Retzius). 

The nerve fibres composing a fine sensory branch remain medullated until they 
arrive near their peripheral termination, where they lose their medullary sheath. This, 
however, does not take place in all nerve fibres at the same time, for we find repeatedly 
minute branches in which some of the nerve fibres become non-medullated much 

sooner than others. 

In the skin and mucous membranes the minute nerve branches containing one, two 
or more nerve fibres when approaching the surface epithelium are connected into a 
plexus, which is called the subepithelial plexus. The branches of this plexus contain 
generally only non-medullated nerve fibres and vary very much in thickness. They 
represent broader or narrower bands composed of minute fibrils, elementary nerve 
fibrils, since even in the thicker examples the distinction into separate axis cylinders has 
been lost. Each branch possesses a sheath with nuclei from place to place. The 
former is a continuation of the perineurium, the latter either belong to the perineurial 
sheath, or are indicative of nerve corpuscles, the sheath of Schwann of the individual 
nerve fibres having ceased previously. 

The points where several branches of the subepithelial plexus anastomose contain 
occasionally (cornea, skin) angular thickenings ; here the (elementary) fibrils cross each 
other and rearrange themselves ; nuclei are generally more numerously met with in 
these thickenings than in other parts. 

i) In the cornea. 

The nerve trunks entering the cornea give off branches for two different systems 



NERVE TE mil NATION IN THE CORNEA. I2$ 

(Engelmann) : a deep one and a superficial one; the former belongs to the substance 
proper of the cornea, the latter to the anterior epithelium. The larger branches of both 
are invested in an endothelial sheath (Durante, Thanhoffer, Thin), and near their peri 
pheral distribution are composed merely of elementary nerve fibrils 

The minute branches of the deep system dissolve themselves into small 
bundles of elementary nerve fibrils, and ultimately into the individual fibrils- these 
are very characteristic by their exceedingly long and straight course, by their 

more or less rectangular bends and h, r fV.»;. ., 

' ana °y thelr anastomosing amongst themselves 

into a terminal network, the 'deep network.' This network lies close to the Des- 
cemetie membrane, but there are minute fibrils which pass through this latter in an 
oblique manner, and appear to be connected into a further network close to or 
in the Descemetic endothelium (Klein). That there are fine fibrils of the deep 
network that terminate by being connected with the corneal corpuscles (body or 
processes) has been affirmed, denied, re-affirmed, and re-denied. Kuhne 1 ipmann 
Moseley, Lavdowsky, Thanhoffer, Konigstein, Izquierdo and others assume such 
a connection; Engelmann, Dwight, Tolotschinow, Rollett, Klein, Waldeyer and others 
deny it. 

The branches of the superficial system form first a subepithelial plexus (Arnold 
Saemisch) ; the nature of the parts of this plexus has been mentioned above; it may 
be added that within the thicker branches the elementary fibrils are much twisted and 
cross each other in many ways, and appear even to be connected into a network. This 
subepithelial plexus lies a short distance away from the epithelium. Fine branches 
come off from it, they pass in an oblique or vertical direction, as rami perforates, 
towards the lower surface of the epithelium (Cohnheim, Kolliker), where they split up 
into isolated or minute groups of elementary nerve fibrils. In the periphery of the 
cornea these fibrils come off from the perforating branches in small brushlike bundles 
(Cohnheim, Klein). In preparations prepared with chloride of gold die elementary 
fibrils are possessed of minute varicosities, and for this reason a perforating branch 
with the brushlike bundle of beaded elementary fibrils bears a great resemblance to a 
'cat-o'-nine-tails.' 

The elementary fibrils run for a shorter or longer distance close underneath the 
epithelium, they are straight or slightly wavy and anastomose with one another into a 
network, subepithelial network (Klein, Izquierdo). After a longer or shorter course 
they rise perpendicularly or in a slightly oblique direction into the epithelium (Hoyer, 
Cohnheim, Kolliker), where they ascend towards the surface, winding their way between 
the epithelial cells. They give off horizontal fibrils (Kolliker, Klein). The latter anas- 
tomose into a network (deep intraepithelial network, Klein) ; the former also join into a 



u 2 



126 ATLAS OF HISTOLOGY. 

network (superficial intraepithelial network, Klein), the fibrils of which are separated 
from the free surface only by the superficial layer of epithelial cells. 

The nerve fibrils, instead of being connected into a terminal network, are said to end in free 
knoblike extremities on the surface of the epithelium (Cohnheim, Lavdowsky, Krause), or in some 
other special way (Thanhoffer, Inzani) ; according to Hoyer and Izquierdo the terminal fibrils 
branch near, but not at the free surface of the epithelium, and end here freely. 

In all instances the intraepithelial nerve fibrils run in the interstitial substance 
between the epithelial cells, and do not enter into any relation with the epithelial cells 
themselves or their nuclei*. 

2) In the skin. 

Besides the special terminal organs to be described below, viz. the Pacinian 
corpuscles, genital corpuscles, MerkeFs cells, tactile corpuscles of Meissner, &c, 
there is the general termination of the sensory nerves, which is placed in the epidermis 
itself. 

From the subepithelial plexus, mentioned above, fine fibrils, isolated or small groups 
of elementary fibrils, come off, which lie close to the under-surface of the rete Malpighii, 
and after having formed a network with large meshes, the subepithelial network, enter 
the rete Malpighii (Langerhans), where they ascend towards the stratum corneum ; 
on their way, viz. in the rete Malpighii, they give off short branches, which 
anastomose into a network (Podkopaew, Jantschitz). This is probably a terminal 
network. 

As in the cornea, so also in the skin the intraepithelial nerve fibrils lie in the 
interstitial substance between the epithelial cells. 

In the nose of the mole there are bundles of elementary fibrils ascending, in 
special places, into the rete Malpighii (Eimer), they run towards the surface, and each 
fibril terminates here, according to Mojsisovics, in a small knoblike swelling. 

A similar termination has been observed by Mojsisovics in the nose of pig. 

In the skin of frog Ditlevsen described special cells as the end organs of the intra- 
epithelial nerve fibrils. 

In the skin of tadpole the non-medullated nerve fibres dissolve themselves into a 
very dense network of minute fibrils (Klein, Lavdowsky, Leboucq); this network lies 
close underneath the epithelium of the surface, its meshes are much smaller than the 
individual epithelial cells. Included in the network are minute flat branched nucleated 
cells (Klein, Lavdowsky, Leboucq). 

The relation of fine nerves to the hairs in general, and especially to the tactile hairs, 
will be considered in the chapter on the skin. 

Similar to the above is the termination of nerve fibrils in the mucous membranes 



PACINIAN CORPUSCLES. I2? 

covered with stratified pavement epithelium. Here also fine (elementary) nerve fibrils 
enter the epithelium (Chrschtschonovitsch, Elin, Krohn), and ascend towards the super- 
ficial layers, giving off one or the other horizontal branch. It is not quite ascertained 
whether they terminate freely in knoblike swellings or whether they are connected into a 
terminal network. 

Special Terminal Organs. 
A. Pacinian corpuscles. 

These corpuscles, more appropriately called Vater's corpuscles, are oblong more or 
less elliptical or pointed corpuscles, varying considerably in size. They ha^ve a wide 
distribution in man and other vertebrates ; they are most numerously found in the sub- 
cutaneous tissue of the volar side of the hand and foot of man, near the tibia of rabbit, 
in the mesentery of cat, in the beak and near the tibia of birds. 

Each Pacinian corpuscle is connected with a medullatcd nerve fibre which, with its 
thick sheath, represents the stalk of the corpuscle. 

i. The corpuscle proper consists of a great number of capsules placed in a con- 
centric manner around a central elongated clear mass ; it shows, therefore, a concentric 
striation, each stria corresponding to a capsule seen in profile. 

The capsules are thin at the periphery and near the central clear mass ; the corpuscle 
appears, therefore, when seen under a low power, to be more densely striated In the 
parts just mentioned. 

Each capsule is made up of the following parts : (a) a hyaline ground membrane, 
probably elastic ; (6) in this ground membrane are embedded fine connective-tissue fibres. 
These are arranged, either regularly in one or two layers, or irregularly, but always in 
a transverse manner, (c) On the inner surface of the ground membrane is an endothelial 
membrane, composed of a single layer of flattened nucleated endothelial cells. 

The above ground membrane corresponds to the intercapsular ' albuminous fluid ' 
mentioned by most observers ; the capsules are not, at any rate not in the fresh state, 
separated by any fluid, but are in immediate contact with one another (Huxley). 

The endothelial membrane lining the capsules shows, with nitrate of silver, the 
usual network of dark lines (Hoyer) indicative of the outlines of the individual endo- 
thelial cells. That the capsules contain, besides these endothelial cells, also fibrous- 
connective tissue has been known through Henle and Kolliker, Keferstein, Krause, 
Ciaccio, Key and Retzius, and others, but it is chiefly Key and Retzius who have most 
elaborately investigated the structure of the capsules, and various very minute differences 
existing in different Pacinian corpuscles. 

Neighbouring capsules are often branched and connected with one another by thin 
fibres (Huxley, Henle and Kolliker, Keferstein, Hoyer, Ciaccio, and others). 



I2 8 ATLAS OF HISTOLOGY. 

2. The stalk of the corpuscle consists of a medullated nerve fibre of the ordinary 
description, with the addition oi a variable amount of fibrous-connective tissue (Axel 
Key and Retzius) ; outside this is a thin limiting membrane, and further a number of 
lamellae with endothelium between them. These lamellae pass directly into the peri- 
pheral capsules of the Pacinian corpuscle (Krause, Schafer). 

3. In order to reach the central clear mass the nerve fibre has to perforate the 
capsules. This section of the nerve may be called the ' intermediary part/ viz. lying 
between the stalk and the central clear mass. 

This intermediary part consists of a prolongation of the medullated nerve fibre, 
more or less wavy, around it a very narrow zone of a transparent substance. Its 
boundary is formed by the limiting membrane just mentioned ; to this latter are fixed 
the capsules that arc perforated by the intermediary part of the nerve (Ciaccio, Schafer). 

4. The central clear mass is a relatively thin cord, consisting of: (a) The 
cylindrical terminal fibre, being the axis cylinder of the nerve fibre. The medullary 
sheath and sheath of Schwann cease at the entrance into the central clear mass. This 
axis cylinder is just like other axis cylinders, finely striated in a longitudinal manner, 
being composed of minute primitive nerve fibrils. Generally near the distal end of the 
central clear mass, occasionally much sooner, the axis cylinder divides into two or more 
small branches of different thicknesses. As a rule, in man and mammals, these branches 
end in a pear-shaped, fungoid, spherical or irregular mass, terminal bud (Key and 
Retzius), containing the terminations of the primitive nerve fibrils of the axis cylinder 
(Grandry). Occasionally the terminal fibre ends in a pointed or fringed manner 
(Izquierdo). The terminal buds show, especially in man and cat, a more or less distinct 
subdivision into small bodies, but without nuclei. The substance of these buds is a dense 
network of minute fibrils, and may therefore be regarded as a terminal network, not to 
be confused with a network of coarse nerve fibres said to exist in the corpuscle proper 
(Paladino, Beale). 

(6) Besides the terminal fibre and terminal buds, the central clear mass contains a 
transparent hyaline or slightly (longitudinally) striated matrix, and(r) the limiting mem- 
brane, both continued from the stalk. Rows of nucleus-like bodies may be seen occa- 
sionally in the peripheral part of the central clear mass. The transparent matrix and 
limiting membrane extend, in some rare instances, in the shape of a longer or shorter 
pointed process (Key and Retzius), beyond the terminal buds. 

The Pacinian corpuscles contain between the capsules capillary blood-vessels, and 
occasionally a few plasma cells. 

In some instances (mesentery of cat) a minute artery is seen to enter the Pacinian 
corpuscle opposite the nerve stalk, and having penetrated to near the distal extremity 



END- BULBS OF CONJUNCTIVA 
one nervous and one vascular. swiks, 

^ ^r apsi " ar *"* occasiona% pre!ent is "-* ■ **— <>«>- 

A The end bulbs of the conjunctiva. 

These were discovered by Krause nnrl im I™ t^ 

f , ■ A , , * ^"se, and are known as Krause's end-bulbs. Thevare 

found, th e deeper layer of the conjunctiva of the eyeba „, ^^ near ^ JJJ 

r. In the calf they are oblong, elliptical, or cylindrical, or spindle-shaped straight 
or curved corpuscles ,n which a medullated nerve fibre, after a longer or shorter 
t_. Th,s . an ordinary mediated nerve fibre, possessed of a shea! f 
Schwann, nerve corpuscles, and Ranviers nodes ; it contains in addition a thicker or 
thinner laminated outer or Hen.es sheath, with flattened nucleated cells. This latt 
passes on as the capsule of the end-bulb. Inside the capsule lies a transparent o 
oft v longitudmally striated cylindrical or spindle-shaped mass, representing 

ie h h ( T ' KCy "" RetZU,S) - ^ thC «* °' ^ "- * terminal 
fibre, winch is a prolongation of the axis cylinder of the nerve fibre. It terminates 

generally in a pom ted or rounded extremity, occasionally in a budlike enlargement 
similar to that m the Pacinian corpuscles (Key and Retzius). 

2. In man they are spherical or elliptical, and, like those in the calf, possess a special 
capsule ; this shows the same structure as that in the bulbs of the calf, being also a 
contmuafon of the sheath surrounding the medullated nerve fibre. According to Key 
and Retzius, this latter on entering the bulb .oses in some instances its medullary sheath 
and the axis cylinder having divided into two or more branches ends in the matrix of 
the bulb. In many other cases the nerve fibre retains its medullary sheath, and becomes 
greatly convoluted, but ultimately loses the medullary sheath, and its axis cylinder 
having divided into thin branchlets terminates in the matrix of the bulb. 

The matrix is a granular mass containing larger and smaller spherical or oval nuclei 
but there are no definite cell boundaries to be perceived between the nuclei (Key and 
Retzius). This granular mass is in reality a dense network of fine fibrils, in which the 
primitive fibrils of the axis cylinder and its branches terminate. 

C. The end-bulbs of the genital organs. 

Fick, Kolliker, Bense, and others, and especially Krause, demonstrated peculiar end- 
bulbs in the penis and clitoris ; each end-bulb is connected with a medullated nerve fibre. 



i 3 o ATLAS OF HISTOLOGY. 

These end-bulbs represent simple or compound elliptical or cylindrical corpuscles, 
situated in the corium and mucosa, and possessed of a capsule of nucleated mem- 
branes. This capsule is either simple or composed of several membranes, but it is 
always a continuation of the tissue in which the nerve fibre is embedded. Generally 
one, occasionally two, medullated nerve fibres enter the corpuscle, and at the point of 
entrance lose their medullary sheath. According to Key and Retzius the axis cylinder 
becomes convoluted in a more or less complicated manner, and finally terminates 
in several small branches, each possessed of a spherical or oval granular end-swelling. 
The convolutions of the branches of the axis cylinder represent the bulk of the end-bulb. 
There are always a (e\v nuclei present amongst these convolutions. 

According to Izquierdo the genital corpuscles of the clitoris of rabbit are numerous, 
broad and simple, while those of the vaginal mucous membrane of the same animal 
are few, narrow and divided. The bulk of the corpuscle is not made up of convolutions 
of the axis cylinder, but either of granular nucleated cells or a fibrous matrix. The latter 
is derived from the former, and accordingly we find corpuscles the matrix of which 
is in different intermediary stages. The nerve fibre does not end in a swelling, but 
having become thinner, terminates in a pointed manner. 

D. The end organs of the beak and tongue of birds. 

These are either of large size, situated in the depth, and formed on the plan of Pacinian 
corpuscles, slightly modified ; they are then called Herbst's corpuscles ; or they are small 
spherical or oval budlike swellings, situated more superficially in the immediate neigh- 
bourhood of the epithelium ; they have been first seen by Grandry, but fully investigated 
by Merkel, and are therefore appropriately called Merkel's end-bulbs. They appear as 
lateral enlargements at the end of a medullated nerve fibre. The enlargement is pos- 
sessed of a nucleated and laminated capsule. The contents of the capsule, i.e. the 
matrix of the end-bulb, consist of a variable number (2-5) of transparent large cells, 
slightly flattened, each with a nucleus, and arranged in a vertical row. 

The medullated nerve fibre loses its medullary sheath when entering the end-bulb. 
Those who have specially investigated the mode of the termination of the axis cylinder 
differ on this point : while some (Merkel, Henle) regard the above transparent cells — 
Merkel's ' tuch-cells ' — as the true terminal organs of the axis cylinder, others (Key 
and Retzius, Ranvier, Hesse, Izquierdo) consider the disc, or discs, situated between the 
broad surfaces of two adjacent cells (disc tactil, Ranvier ; Tastplatte, Hesse) as the 
real termination. 

E. According to Merkel, there exist similar end organs, viz. 'tuch-cells/ also in the 
skin of man and other mammals (nose of pig, especially the small tuch hairs of the nose 



NERVE TEXMWATW „ UKSTWtD MUSCLE. ,„ 

of pig. Died). They are situated either in the tissue r»f ,1, 

the epithelium. The y occur as simple or J^^Z^ "*" "T 
large and slightly flattened transparent nucle ted ce„s 2 lar " t , ^ ^ S "^'' 
the beak and tongue of birds) enclosed in a r *"*** ° f 

forming a direct continuity J h . ££* Z^^ ££." «"*» * 
a capsule several small cells. The 'tactile' or M C ° nUUa ^ 

especially in the papillae of the skin 1 T ^^ ^ ^ 

" ° f the Rngers of man - «e such multicellular end 



£ Termination of nerves in unstriped and striped muscle fibre, 

The t.ssue of muscle is richly supplied with nerves. Their distributi „ ■ 
considerably in striped and unstriped muscle. ^stribufon var.es 

i. In unstriped muscle. 

The nerve branches are composed of non-medulkted nerve fibres c-rch „f „, 
(nerve branch, possesses an endo.heha, shch , t hev divide huo in vi tZ 

T3rr„r"° ders ' * h s "- ~» - **«-*-»*.*<*.. «u 

fi Ms Tb s C0 " S ' S " n!r '" "" '"'""^ ""' re <™«™ °f "* Prin,i,ive 

fibr.k Th,s plevus represents ,he ground plexus of Arnold. Its branches are pos 

::::,;: b ; ,o ° 8ing either ,o mm •"*-*■ °< - ■— — ■?* - 

tinuous with the above endothelial sheath. 

The branches of the ground plexus divide into fibres of various thicknesses, still 
possessed of nucle, indicative of nerve corpuscles; these fibres form another plexus 
the intermediary plexus of Arnold. This belongs to the individual bundles of the' 

bundle's mUS fibl ' eS ' WherCaS thC gr ° Und PlCXUS aPPCrtainS t0 a *"* ° f mus * 

The fibres of the intermediary plexus, however thin, are always compound, being a 
smaUer or larger bundle of primitive fibrils. They give off the latter, viz. the primitive 
totalis, which pass into the interstitial substance that separates the individual muscle cells ■ 
ere they run for a longer or shorter distance, and anastomose with their neighbours 
by transverse or oblique fibrils into a real network. These fibrils represent the inter- 
muscular fibrils of Klebs. It is not definitely settled whether they themselves are the 
terminal fibrils (Lowit), or whether they send off still finer branches that penetrate into 
the nucleus of the muscle cells. Frankenhauser Jets them terminate in the nucleolus, 
undiv,ded if one, divided in two if there are two nucleoli. According to Arnold they 
termmate in the nucleolus, but so that this latter is only a nodal point in the ultimate 
or intramuscular network. Elischer describes the nerve fibrils as terminating on the sur- 
face of the nucleus with a small swelling. 



x 



r 3 2 ATLAS OF HISTOLOGY. 

A termination of nerve fibrils in the nucleus of the muscle cells is not improbable, 
although it does not take place in a nucleolus. 

The intermuscular fibrils are occasionally connected with a nucleated pear-shaped, 
spherical, or spindle-shaped swelling similar to a ganglion cell (Klebs, Gscheidlen). 

2. In striped muscle. 

The nerve bundles ensheathed in their perineurium are situated in the connective 
tissue separating groups of bundles of muscle fibres, and are composed of medullated 
nerve fibres of the ordinary description. These branches form a plexus, ground plexus. 

Isolated and small groups of nerve fibres come off from this plexus ; they are 
conspicuous by their dividing into two, seldom three, medullated nerve fibres, and are 
also connected into a plexus, intermediary plexus, destined for the bundles of muscle 
fibres. 

Isolated medullated nerve fibres enter the individual muscle fibres in an oblique or 
vertical manner, the sheath of Schwann of the nerve fibre becoming fused with the 
sarcolemma, while the axis cylinder, having lost its medullary sheath, passes within the 
sarcolemma (Rouget, Kiihne). 

In most animals, man included, the axis cylinder then branches into several 
thin fibres, forming a network with one another ; these fibres remain on the surface 
of the muscle substance proper, but lie embedded in a granular platelike mass, the 
nerve end-plate of Kiihne, containing numerous oval nuclei. These nuclei are of 
three different kinds (Ranvier) : some belong to the outer or Henle's sheath of the 
nerve fibre ; others correspond to the nerve corpuscles ; and finally there are nuclei 
that belong to the granular matrix of the end-plate. When such an end-plate is 
viewed in profile, especially in a more or less contracted muscle fibre, it presents itself 
as an elevation, Doyere's mount. 

In batrachia the medullated nerve fibre, after having lost its medullary sheath, 
divides into several longer or shorter thin fibres (Kolliker), which terminate apparently 
in a pointed or rounded extremity ; oblong nuclei are attached to them. These fibres 
are on the surface of the muscle substance, but within the sarcolemma (Kiihne, 
Krause, Engelmann, Waldeyer, Calberla, and others). According to Kiihne the muscle 
fibres of batrachia do not possess a granular platelike mass in which these fibres termi- 
nate, but Krause, Waldeyer, and Axel Key have shown that there is no such distinction, 
the batrachian muscle fibres showing also a granular platelike matrix for the intra- 
muscular branches of the axis cylinder. Arndt has shown that in batrachia both modes 
of nerve terminations occur. 

There are end-plates, into which enter two nerve fibres (Krause, Arndt). The end- 
plates differ in size ; generally more than one end-plate belongs to a muscle fibre. 



NERVE TERMINATION IN STRIPED MUSCLE. , 33 

According to Arndt they are always numerous in the muscle fibres of vertebrates, man 

and mammals included. 

It is not decided whether the intramuscular nerve fibres terminate in the end plate 
(Kuhne, Ranvier, and others), or whether fine fibrils pass beyond this latter qL* 
Engelmann, especially Arndt, T. Gerlach) ; that they do not do so is maintained by fhe 
most recent investigators (Fischer, Ewald, Biedermann). 

According to Arndt the end-plate and end-divisions of the motor fibres are alone 
intramuscular ; with them are connected nerve fibres which join into a plexus which is 
extramuscular, i.e. situated outside the sarcolemma of the muscle fibre such as had 
been seen by Kolliker, Beale, Krause, and others. Arndt regards them as sensory 
nerve fibres. 

According to L. Gerlach, the bundles of the muscle fibres of the heart (of frog) 
possess a network of fine non-medullated nerve fibres, perimuscular network Fine 
fibrils come off from this and form a network between and around the individual muscle 
fibres, intramuscular network ; but only seldom do these nerve fibrils join the substance 
of the muscle fibres. According to Fischer, however, the nerve fibrils terminate only 
in the above network, viz. between the muscle fibres, without ever joining the substance 
of these latter. 

G. Nerve termination in tendons. 

Tendons possess numerous medullated nerve fibres, which, in some instances, are 
distinguished by their repeated division and formation of a plexus (Sachs, Rollett, Gempt). 
They run generally a long and straight course in conformity with the arrangement of the 
tendon bundles (Golgi). The termination of the nerves is effected in special organs 
(Sachs, Rollett, Golgi), which are more numerous near the muscle than in other parts 
(Golgi). It takes place in two different ways : (a) tie nerve fibre loses its medullary 
sheath, and its axis cylinder branches into several fine brandies, these dissolve themselves 
into very short elementary fibrils, which form a dense network (Sachs) ; (i) the ultimate 
fine nerve fibrils are occasionally embedded in a hyaline or granular nucleated ground- 
substance (Rollett), and thus an end organ is produced in some respects similar to an 
end-plate in muscle fibres. 

In some tendons there are, in addition, nerve fibres that terminate in the shape of 

peculiar end-bulbs (Sachs), similar in structure to the end-bulbs of the conjunctiva (Golgi). 

In the tendon sheaths Rauber describes as 'synovial bulbs ' peculiar end-bulbs of 

medullated nerve fibres, similar in structure to the Pacinian corpuscles, but much 

smaller. 

In the aponeurosis of the cutaneo-pectoral muscle of frog Tschiriew found the nerve 



X 2 



i 3 4 ATLAS OF HISTOLOGY. 

fibres forming a network with large meshes; from this fine fibrils come off and terminate 
in small knoblike swellings. 

H. Termination of nerves in blood-vessels. 

The nerve fibres of the microscopic arteries and veins are derived from minute 
bundles belonging to the adventitia ; they are non-medullated fibres possessed of a sheath 
of Schwann and the corresponding nerve corpuscles ; they divide into smaller fibres 
which form a plexus, ground plexus. 

The nodes of this plexus are, in many places, triangular, and contain one or more 
angular nuclei. From the ground plexus are derived fine fibres, which belong to the 
muscle coat of the vessel (Klein, Gonjaew, Gscheidlen) ; they form a plexus, inter- 
mediary plexus, which is denser in arteries than in veins (Klein, Gscheidlen). The 
fine fibrils coming off from this last plexus are elementary fibrils, and run between the 
individual muscle cells. 

In capillary arteries and capillary veins there are a few fine nerve fibres, with 
nuclei from place to place (indicative of nerve corpuscles), which accompany the vessel 
(Beale, Klein, Tomsa), and in some places form a more or less dense network of primi- 
tive fibrils (Klein, Gonjaew, Jantschitz). 

In some localities the nerve branches belonging to a vessel are provided with small 
ganglia (F. Darwin for the urinary bladder, Jantschitz for the dura mater). 

PLATE XXIV. 

All figures of this plate are drawn under a magnifying power of about 400. 

Fig. I. From a preparation of frog's cornea stained with chloride of gold, showing 
the network of elementary (beaded) nerve fibrils situated near the Descemetic mem- 
brane, and coming off from a large branch possessed of a sheath (marked pink). This 
large branch represents a bundle of elementary fibrils ; they appear to be connected 
into a network while still within that sheath. 

Fig. II. From a preparation of rabbit's cornea stained with chloride of gold, 
showing portions of two large branches of the subepithelial plexus. They consist of 
elementary nerve fibrils. Short branches, perforating branches, are derived from them ; 
they split up into brushlike groups of elementary beaded fibrils, connected into a net- 
work, siibcpitJielial nchuark. 

Fig. III. From a similar preparation as the preceding figure, representing a portion 
of the subepithelial plexus. At the point of anastomosis of the branches of this plexus 
are triangular thickenings, and it is just here where the constituent elementary fibrils are 






p.. : 



in 











ATLV 



XXV. 











UX\ ^ 'J 




vu 










' 



i ■ . 



VIII 



% 





XT 







XIII. 






■ 



. 



PLEXUS OF FINE NERVE FIBRES. r« 

best seen. The isolated fibrils in the left portion of the figure are those that run 
immediately underneath the epithelium, and are connected into the subepithelial network. 

Fig. IV. From a preparation of the submucous tissue of large intestine of toad, 
stained in chloride of gold ; showing part of a plexus of non-medullated nerves. All 
branches consist of elementary fibrils. Three nuclei are shown that belong to nerve 
corpuscles ; the sheath is not represented. 

Fig. V. From a preparation of tadpole's tail, prepared with chloride of gold, 
showing the plexus of larger and smaller nerve fibres. The nuclei are indicative of 
nerve corpuscles ; the sheath is marked by a slight pink tint. 



PLATE XXV. 

Figures VI. VII. IX— XI. are copied from Key and Retzius. 
Fig. VI. Two capsules of a Pacinian corpuscle of man ; an endothelial membrane, 
lining a third capsule, is represented on the right as if viewed from the surface. Magni- 

fying power 450. 

Fig. VII. Termination of the axis cylinder in the central clear mass of a Pacinian 
corpuscle of the mesentery of cat. 

The axis cylinder divides into 4 to 5 branches, each of which terminates in a 
globular end-bud. 

The capsules next the central clear mass are represented in outline only. Magni- 
fying power 750. 

Fig. VIII. A Pacinian corpuscle of the mesentery of cat, as seen under a magni- 
fying power of about 100. 

The stalk consists of the nerve fibre with its thick outer sheath. The peripheral 
capsules of the Pacinian corpuscle are continuous with the outer sheath of the stalk. 
The intermediary part becomes much narrower near the entrance of the axis cylinder 
into the central clear mass. A hook-shaped termination with the end-bulb is seen in the 
upper part. A blood-vessel enters the Pacinian corpuscle, and approaches the end- 
bulb ; it possesses a sheath which is a continuation of the peripheral capsules of the 
Pacinian corpuscle. 

Fig. IX. An end-bulb of the conjunctiva of man. 

The medullated nerve fibre shows a node of Ranvier, a sheath of Schwann, and a 
nerve corpuscle; outside these is another sheath, the sheath of Henle. The end-bulb 
itself possesses a capsule continuous witli the sheath of Henle ; the matrix of the end- 
bulb is a granular substance with nuclei. The nerve fibre on entering loses its 

Y 



6 ATLAS OF HISTOLOGY. 

medullary sheath, while the axis cylinder divides into several branches ; these are more 
or less convoluted and lost in the matrix. Magnifying power about 700. 

Fig. X. An end-bulb of the glans clitoridis of rabbit. 

The nerve fibre possesses an outer sheath of Henie, which is continuous with the 
capsule of the end-bulb. After having lost its medullary sheath, the axis cylinder enters 
the end-bulb, becomes much convoluted, and terminates in several small branchlets, 
possessed of knoblike swellings. Magnifying power 570. 

Fig. XL Summit of a Pacinian corpuscle of finger of man, stained with nitrate of 
silver, to show the endothelial membranes lining the capsules. Magnifying power 
about 220. 

Fig. XII. Nerve termination in unstriped muscle of the muscularis mucosa? of 

large intestine of toad, after staining with chloride of gold. 

* The larger fibres belong to the intermediary plexus) two nuclei are shown indicative 

of nerve corpuscles. 

The fine fibrils run between the unstriped muscle cells— only their oblong nuclei 
are indicated here— and terminate in a network. Magnifying power about 350. 

Figures XIII. and XIV. copied from Arndt, Archiv f. mikr. Anatom. IX. 

Plate XX. 

Fig. XIII. Two striped muscle fibres of the hyoglossus of rana temporaria. 

Magnifying power about 600. 
a. Nerve end-plate. 
//. Nerve fibres leaving the end-plate. 

c. Nerve fibres terminating after dividing into several branches. 

d. A nucleus in which two nerve fibres anastomose. 

Fig. XIV. Nerve end-plate in a striped muscle fibre of rana temporaria. Magni- 
fying power about 1000. 

A medullated nerve fibre terminates, after dividing into several branches, in the 
nerve end-plate ; this is a granular mass containing numerous nuclei. 



mg 



CHAPTER XIX. 

BLOOD-VESSELS. 
i. Capillary Blood-Vessels. 

The smallest and at the same time the simplest vessels are the capillaries, be 
minute tubes the wall of which is a thin elastic endothelial membrane, that is, 
single layer of nucleated cell-plates (Hoyer, Auerbach, Eberth, Aeby, and others). 

Like other endothelial membranes, its individual cells are united by an albuminous 
interstitial cement-substance, which in silver-stained specimens appears as dark lines 
separating the cells. The shape of the cells is more or less elongated, with pointed 
extremities, and their outline smooth or sinuous. This depends, however, in a certain 
measure, on the state of distension or contraction of the capillary. Their substance is 
in the fresh state hyaline, but under certain conditions shows, just like the endothelial 
cells of serous membranes, a hyaline ground-plate, and in it a network of fibrils. 

Each cell possesses an oval flat nucleus, situated either about the middle of the cell 
or near one extremity ; the nucleus contains within a well-defined membrane an intra- 
nuclear network (Flemming, Klein); in adult capillaries this intranuclear network is 
uniform and does not contain any thickenings or nucleoli. 

When capillaries are abnormally distended, as in inflammation, the interstitial 
cement-substance is liable to give way in many places ; in consequence of this, minute 
openings appear (stigmata, Arnold), which become gradually enlarged into stomata. 
When injecting such vessels, an escape of injection matter (Winiwarter) may take place 
through these openings. They are likewise probably the places where, under inflam- 
matory conditions, diapedesis of coloured (Strieker) and emigration of colourless 
corpuscles (Cohnheim) into the surrounding tissue occurs. 

If capillary vessels, through which emigration of colourless blood-corpuscles ha 
been going on, be stained with nitrate of silver, it is seen that the emigration is limited 
to the interstitial cement-substance of the endothelial wall (Purves). 

Besides the endothelial wall, the (larger) capillaries in some localities possess a 
special outer sheath, or adventitia, which is a network of branched connective-tissue 
cells (hyaloidea of frog, chorioidea of mammals, IvanofT, Eberth, and others), or a 
complete endothelial membrane (pia mater of brain and cord, Key and Retzius ; retina, 



. , o ATLAS OF HISTOL OG i '. 

Eberth ; serous membranes, Klein), or a network of fibres and membranes (lymphatic 

glands, His). 

Capillaries vary in size in different localities and in different animals. Thus the 

capillaries of the brain and of the lung in man and mammals are smaller than those of 

the liver, and much more conspicuously so than those of the bone-marrow. The lumen 

of capillary blood-vessels varies according to whether this latter is more or less distended 

with fluids (blood or injection matter), or whether it is contracted or collapsed. 

In young capillaries, both of normal and pathological tissues, the wall is possessed 

of solid threadlike shorter or longer nucleated protoplasmic processes (see below), and 

is capable of active contraction (Strieker). In consequence of this, the lumen may 

become altogether (temporarily) closed, and the vessel contracted into a thin apparently 

solid thread (Strieker). 

The wall of all capillary vessels in the adult state forms a direct connection with 
the processes of the connective-tissue corpuscles of the surrounding tissue (Klein, 
Altmann) ; the significance of this relation will be considered in connection with the 
lymphatic vessels. 

Capillary blood-vessels are connected into a network, the distribution and arrange- 
ment of which varies in different organs, and will be specially described with the latter. 

2. Arteries. 

Following a capillary vessel towards the arterial system, the following appearances, 
besides the increase in breadth, indicate its having changed into an arterial branch : 
(a) the presence of a permanent outer sheath, or adventitia, in the shape of a single layer 
of flattened nucleated cells, either branched and forming a network (see above), or un- 
branched and forming a continuous endothelial membrane. (S) The appearance of short 
unstriped muscle cells as a special layer, media, transversely on the long axis of the 
vessel ; these muscle cells occur in groups, placed on alternate sides of the vessel. 
The reason is probably this : the length of the uncontracted muscle cells being about 
equal to the circumference of the vessel, the muscle cells, when contracting, are thus able 
to narrow uniformly the vessel. In somewhat larger arterial branches the larger circum- 
ference requires more than this, and the muscle cells form a continuous circular layer in 
all parts of the vessel. (e) Inside the muscle layer is a delicate hyaline elastic 
membrane, the intima. (d) The inner boundary is formed by the endothelium, being a 
continuation of the endothelial wall of the capillary vessel. 

The endothelial plates of all arterial vessels are much elongated, with more or less 
straight outlines. 



STRUCTURE OF ARTERIES. 

The transition of a capillary vessel into an artery is not sudden but gradual and it 
is by the muscle cell that we are able to distinguish definitely the latter from the former 
The part of the vessel that shows the gradual transition from a purely capillary vessel 
into one with all the above attributes is called a capillary artery. 

Following these minute vessels into larger arterial branches, we notice the following 
changes : (a) besides the cells representing the outer sheath, or adventitia, there is a 
variable amount of fibrous-connective tissue in the shape of smaller or larger bundles 
The larger the vessel the larger the amount of fibrous tissue. In arterial trunks 
(carotis, subclavia) the adventitia is a complex connective-tissue membrane, inasmuch as 
the bundles are arranged into groups or trabecules crossing each other ; between them 
are the interfascicular lymph spaces, containing branched connective-tissue cells, and 
also networks of elastic fibres arranged parallel to the long axis of the vessel. These 
elastic fibres are well seen in large arterial trunks (carotis, subclavia, mesenterica) ; they 
are more numerous, and at the same time thicker, in the inner portion of the adventitia, 
that is, nearest the media. 

(i) The muscle cells form a continuous membrane in the media or muscle coat 
proper: the larger the artery the thicker this latter. Most of the muscle cells are 
arranged transversely, but in larger arteries there are small bundles of oblique or even 
longitudinal muscle cells. While in the smallest arterial branches the muscle cells are 
arranged in a single layer, as the vessel becomes larger, also the number of these layers 
increases. In a section through a hardened artery, that had been kept distended by blood 
or otherwise, the muscular coat will appear much thinner than if the vessel had been 
allowed to shrink ; and it is important to bear this fact in mind when comparing the 
muscular coat of two arteries. In the arterial trunks the individual layers of muscle fibres 
are separated from each other by hyaline elastic membranes and elastic networks. In large 
arteries (carotid, mesenteric) these interstitial elastic membranes and elastic networks 
become so increased that they form a conspicuous portion of the media. The arrange- 
ment is then so that thin strata of muscle cells are separated from one another by 
thinner or thicker horizontal or oblique elastic lamellae, to which are attached networks 
of fine elastic fibres ; these latter enter also into the individual layers of muscle 
cells. 

The elastic lamellae are generally of the nature of fenestrated membranes of Henle; 
that is to say, a more or less homogeneous membrane with larger and smaller holes. 
This membrane is in reality a network of broad more or less confluent elastic fibres, 
the meshes of the network being the holes of the fenestrated membrane. 

The muscle cells of the media are relatively short, and in arterial trunks are more 
or less branched at their extremities. In the largest arteries of man, such as aorta, 

Z 2 



I4 o ATLAS OF HISTOLOGY. 

carotis, subclavia, mesenterica, &c, most muscle cells are more or less flattened, and 
their outline not smooth but beset with small processes. 

When the muscle cells are viewed in transverse section (that is, in a longitudinal section 
through the vessel), they differ in so far from those of a transverse section through ordinary 
unstriped muscle tissue, such as of the intestine, bladder, uterus, &c, as many more muscle cells 
are found showing a nucleus in the former than in the latter ; the reason being that the muscle 
cells of the arteries are much shorter than in other organs, and hence more muscle cells are 
cut through the nuclear portion in a given transverse section through the former than in one 
through the latter. 

In the large arterial trunks also a certain amount of connective tissue is present 
In the media, in the form of small branched flattened nucleated connective-tissue cells, 
embedded in a hyaline albuminous interstitial substance. 

The media is separated from the adventitia by a special elastic membrane (external 
elastic coat, Henle), conspicuous only in larger arteries, as carotis, mesenterica, renalis, 
hepatica, cruralis, &c. 

(c) The intima is very distinct in all arteries; in the minute branches it is a thin 
bright elastic membrane, much folded when viewed in a transverse section through a 
contracted vessel. It is thickened on its outer surface by longitudinal elastic fibres 
forming a network. In the larger branches the intima is laminated, the laminae being 
(longitudinal) fenestrated elastic membranes, between which pass (longitudinal) networks 
of elastic fibres. In the arterial trunks there are branched connective-tissue corpuscles 
present between the laminae constituting the intima. 

The large arteries possess on the inner surface of the intima, underneath the lining 
endothelium, a special connective-tissue membrane, the inner longitudinal fibrous layer 
of Remak, Kolliker, Gimbert, Eberth, and others. This subendothelial connective-tissue 
membrane consists chiefly of longitudinal bundles of fibrous-connective tissue, and 
between them are anastomosing branched connective-tissue cells. But even small arterial 
branches seem to possess a prolongation of this inner connective-tissue membrane, 
in the form of a single layer of branched cells separating the intima from the lining 
endothelium. 

(d) The endothelial cells lining the lumen of large arterial trunks are less elon- 
gated than those of the minute branches, but this depends on the state of contraction of 
the vessel ; for when this is contracted, the cells appear more elongated and thicker 
than when not contracted. 

The Aorta differs only slightly, in structure, from other large arteries; the fol- 
lowing points deserve to be mentioned : — 

{a) The adventitia, composed of fibrous-connective tissue, is relatively very thin. 



STRUCTURE OF AORTA. , 4 , 

(b) The media contains, between thin transverse muscular strata, thick elastic 
membranes ; these are placed horizontally or obliquely, and are laminated, being composed 
of several Henle's fenestrated membranes, and in addition to them there are networks 
of fine elastic fibres. In the ascending aorta and the arch there is a small inner section 
of the media that differs from the rest, in so far as the muscle cells are arranged in 
small groups, running either longitudinally or obliquely ; they are separated by thick 
cylindrical longitudinal elastic fibres which are much branched, and in some places very 
close or even confluent. Between them are networks of fine elastic fibres running lonei- 
tudinally or obliquely. 

This inner portion amounts in the ascending branch and the arch to about an 
eighth or tenth of the whole thickness of the media, and gradually passes into the outer 
part, the muscle cells becoming transverse, and the thick elastic fibres becoming confluent 
into membranes placed horizontally or obliquely. But there are groups of longitudinal 
muscle cells also in the outer part of the media, especially near the adventitia. 

The muscle cells of the aorta are much branched, flattened, and short, but varying 
considerably in their broad diameter. 

A certain amount of connective tissue, chiefly accompanying small blood-vessels, is 
to be found in this coat. 

(c) The intima of the aorta is similar in structure to that of other large trunks, 
except that it is thicker, and that it contains an appreciable amount of connective tissue 
added to it ; also the subendothelial longitudinal connective-tissue membrane is well 
developed. In the ascending aorta and the arch the intima is distinctly laminated, the 
laminae being composed of elastic fibres, and between them is an appreciable amount of 
connective tissue, chiefly in the form of branched connective-tissue corpuscles ; the 
subendothelial membrane is here thickest. 

(d) The endothelium does not differ from that of the arterial trunks. 



Besides the aorta there are other arteries In man and mammals that possess 
longitudinal and oblique bundles of unstriped muscle fibres. According to Remak, 
Kolliker, Eberth, and others, the arteria lienalis, renalis, femoralis, mesenterica, 
axillaris, poplitea, &c, possess longitudinal muscle bundles in the adventitia, and, 
according to Remak and Eberth, the arteria hepatica, lienalis, cruralis, and mesen- 
terica possess them also in the media. This is, however, denied by Bresgen : 
according to this observer there are no longitudinal muscles in the mesenterica inferior 
lienalis, gastro-duodenalis, brachialis, radialis, and cruralis. Bardeleben, on the other 
hand, maintains an inner longitudinal muscle coat for all large and middle-sized arteries. 



r 42 ATLAS OF HISTOLOGY. 

The basilar artery has no inner longitudinal muscles, whereas the subclavia has them 
exceptionally well developed. The umbilical artery possesses on the inner surface of the 
media, of the ordinary structure, a continuous longitudinal muscle coat, and also on the 
outer surface of it (media) are a few longitudinal muscle bundles (Eberth). 

The different coats bear a definite relation to one another : the adventitia is 
relatively thickest m the minute arteries, being here nearly as thick as the middle coat, 
it is inferior in thickness to the media in middle-sized and large arteries ; in the latter it 
amounts only to a fraction of the media, and in the first part of the aorta it is reduced 
to a very delicate membrane. The media is in all arteries, in virtue of its thickness, the 
most conspicuous coat. The intima increases in thickness towards the aorta ; in the micro- 
scopically minute arteries it is a very delicate simple membrane. The endothelium is 
everywhere a single layer of cell-plates. 

3. Veins. 

Following a capillary vessel towards the venous system, we first come upon the 
capillary veins : these are broader than the former, and possess, just like the capillary 
arteries, a delicate nucleated membrane as adventitia and a very thin membrane, com- 
posed of a network of longitudinal fine elastic fibres, as intima. The lining endothelial 
cells are somewhat shorter and broader than those of the capillaries, and their outlines 
more or less sinuous. What has been said as regards stigmata and stomata in the 
endothelium of capillaries holds good also for veins (Arnold). There is no muscle 
tissue, as a media, to be met with in these venous capillaries, and the thickness of their 
wall as compared with the size of their lumen is therefore greatly inferior to that in the 
minute arteries. And this same inferiority persists in all veins, viz. their wall is much 
thinner, and their lumen larger, than in the corresponding branches of the arterial system. 

As the capillary veins pass into larger branches, the adventitia increases in thick- 
ness by the addition of bundles of fibrous-connective tissue, which are accompanied 
by the ordinary flattened connective-tissue corpuscles. The (microscopically) large 
branches of veins show the first traces of a muscular media, the muscle cells being 
placed transversely ; the intima is only slightly thicker than in capillary veins. 

In the venous trunks we find (a) a relatively thick adventitia, composed chiefly of 
longitudinal and oblique trabecular of fibrous-connective tissue, in the interfascicular 
spaces are the ordinary connective-tissue corpuscles ; thicker and thinner elastic fibres 
run pre-eminently in a longitudinal direction and form a network. 

(b) The media contains, in most instances, transverse bundles of unstriped muscle ; 
they never form such continuous layers, and are not separated by elastic membranes, as in 
arteries, the bundles being separated from each other chiefly by fibrous-connective tissue. 



STRUCTURE OF VEINS. , 43 

(c) The intima is always a very thin elastic membrane ; this is composed of 
networks of longitudinal fibres, more or less confluent into a fenestrated Henle's 
membrane. 

The subepithelial (longitudinal) connective-tissue membrane, mentioned in con- 
nection with the intima of the arteries, is generally present in most venous trunks 
in the form of a delicate network of branched cells, but only in some it contains in 
addition slender longitudinal bundles of fibrous-connective tissue. It is of conspicuous 
thickness in the vena poplitea (Eberth). 

(d) The endothelial lining is composed of short, broad, spindle-shaped, flat 
endothelial cells with sinuous outlines. In the venous sinuses of the spleen of man 
and some mammals the endothelial cells are sometimes almost polyhedral, that is, thick 
and short (Klein). 

The valves in veins are folds of the endothelial lining of the whole intima and of 
part of the muscular media; the muscles are slender bundles that run either longi- 
tudinally or transversely (Bardeleben). 

The greatest variety exists amongst the larger veins as regards the distribution ol 
unstriped muscles in their wall. The venous vessels of bone and muscle, and of the 
retina, those of the membranes of the brain and spinal cord, the last portions of th«- 
venous trunks emptying themselves into the cava superior, the vena jugularis interna 
and externa, and vena subclavia have no muscles. 

The veins of the gravid uterus possess only longitudinal (unstriped) muscles. The 
vena cava, azygos, hepatica, spermatica interna, renalis and axillaris possess an inner 
circular and an outer longitudinal muscle coat. The vena iliaca, cruralis, poplitea, 
mesenterica, and umbilicalis possess, between an inner and outer longitudinal, a middle 
circular muscle coat. 

The trunk of the vense pulmonales possesses striped muscle tissue (Arnstcin, Stieda), 
In man they are arranged as an inner circular and an outer longitudinal coat (Stieda), 
and are to be regarded as a continuation of the striped muscle tissue of the left auricle, 
with which they are identical in structure (Stieda). The intima of the vena? pulmonales 
of man is a connective-tissue membrane, containing circular bundles of unstriped muscle 
cells (Stieda). 

Hoyer showed a direct communication of minute arteries with veins, without the 
intervention of capillaries, to exist in various places, as in the matrix of the nail, in 
the tip of the nose and tail of some mammals, in the tip of the fingers and toes of 
man, in the margin of the earlobe of dog and cat, and especially of rabbit. According 
to the same observer, this anastomosis occurs either with veins that have no muscular 



i 4 4 ATLAS OF HISTOLOGY. 

media, but consist only of an endothelial lining, and a connective-tissue adventitia, as in 
the nail matrix of man, and in the tip of the nose in mammals ; or with veins that 
possess a distinct media of circular muscles, as in the tip of the fingers and toes of man. 



The presence of contractile branched pigment cells in the adventitia of arteries 
and veins of lower vertebrates has been mentioned on a former occasion in Chapter VII. 
Also the presence of sinuous and spindle-shaped dilatations in the minute veins and 
capillaries of some striped muscle fibres of rabbit, as discovered by Ranvier, and the 
spindle-shaped and angular dilatations of the inner (capillary) network of the dura 
mater of the brain, described by Boehm, Key and Retzius, Michel, and others, have 
been mentioned in Chapters XI. (p. 80), and XV. (p. 105) respectively. 

Peremeschko saw similar spindle-shaped dilatations on the vessels of the 
ligamentum nucha? of dog and cat. 

Beale described, many years ago, sinuous dilatations on the capillary vessels of the 
pharynx of frog. 

In the cavernous tissue of the male and female genital organs minute veins form a 
dense plexus in the form of wide sinuous spaces lined by endothelium ; into these lead 
the arterial branches. The wall of these venous spaces is formed by elastic and 
unstriped muscle tissue. 



The adventitia and media of large vessels (arteries and veins) contain a special 
system of nutrient blood-vessels, vasa vasorum ; the arterial and venous branches of 
these lie chiefly in the adventitia, occasionally also in the outer part of the media ; 
the capillaries generally penetrate into the media and near the intima, only seldom also 
into the latter (Koster). In the microscopic arterial branches we meet with capillary 
vessels as a rule only in the adventitia. 

Lymph-spaces are present as intercommunicating interfascicular spaces, containing 
connective-tissue cells, in all coats of arterial and venous trunks. The lymphatics 
attain their greatest development in the adventitia of large trunks (arteries and veins), 
where they form a plexus of more or less tubular vessels. In the smaller trunks they 
form large sinuouslike spaces lined by continuous endothelium. These spaces in the 
adventitia, both of arteries and veins, become occasionally fused into longer or shorter 
continuous lymphatic vessels, ensheathing, as it were, the vessel to a larger or smaller 
extent as a perivascular lymphatic, as is the case with some vessels of the omentum, 
mesentery, and the membranes of the brain, in the hepatic and splenic artery, and in the 
pulmonary vessels. 



DEVELOPMENT OF BLOOD-VESSELS. , 45 

In the large trunks (venous and arterial) there are lymph channels present also in 
the media ; they appear as clefts between the muscle bundles, and communicate with 
the lymphatics of the adventitia (Koster). 

4. Development of Blood-Vessels. 

All blood-vessels in their young state are of the nature of capillaries, that is, their 
wall is a simple membrane consisting of a single layer of nucleated endothelial cells. 
Considerable differences exist as regards the size of these young vessels, the lumen 
of some being many times larger than that of ordinary adult capillaries. When the 
wall of a young vessel exhibits a differentiation into nucleated endothelial plates, and a 
linear albuminous interstitial substance acting as cement of these endothelial cells 
the vessel has already passed the more important stages of its development ; these 
stages, counted backwards, are: (1) the wall of the tubular vessel is an uniform 
membrane, not exhibiting any differentiation yet into endothelial cells and cement- 
substance ; this membrane is protoplasm containing a network of fibrils, the intra- 
cellular network, as mentioned above, and appearing therefore uniformly ' granular,' 
and in it, more or less regularly disposed, are oval nuclei containing the intranuclear 
network. (2) Previous to the above stage the vessel is irregular, being at some places 
much narrower than at others ; while at the latter it is still tubular, at the former 
it will be found quite solid protoplasm with nuclei, and resembling then a nucleated 
protoplasmic thread or band ; this latter contains a smaller or larger number of 
vacuoles, which in some places are more or less close together, and ready to become 
fused. When this happens, the vessel becomes tubular, the above solid protoplasmic 
band or thread being thus hollowed out. When these vacuoles appear and, still more, 
when they increase in number and size, the nuclei previously contained in the centre of 
that solid protoplasmic band are shifted by them (vacuoles) into the marginal portion. 
After the band is converted into a tube, this marginal portion containing the nuclei 
represents the wall of the vessel. 

In this state of solid protoplasm with nuclei, we find not only larger or smaller 
sections of a network of vessels, the rest being composed of already tubular vessels, 
but also such single structures may be met with that are destined to become branches 
of an already tubular vessel. In the latter case, viz. where we have to do with the 
development of a branch, we find it as a longer or shorter nucleated, divided or un- 
divided, solid protoplasmic filament, directly continuous with the wall of the tubular 
vessel. The portions of the thread containing nuclei are, of course, thicker than the 
intervening sections. This thread may be a real outgrowth, a 'sprout,' of the wall of 
the main vessel, and then it may continue to grow; or it may be only a nucleated 

A A 



I46 ATLAS OF HISTOLOGY. 

cell belonging originally to the surrounding tissue, and identical with a connective- 
tissue cell, connected with the wall of the vessel. In both cases the solid pro- 
toplasmic filament becomes hollowed out, either by the lumen of the main vessel 
gradually penetrating into it, or by several distinct vacuoles appearing in it, which, by 
enlarging, become confluent with one another, and also with the lumen of the main 
vessel. Several connective-tissue cells, connected into a network, may, by separated 
vacuolation, and by subsequent confluence of these, give origin to a network of 

capillaries. 

In the embryo we meet with large sections of the vascular system, that are at first 
represented merely by solid nucleated protoplasmic cells, either spindle-shaped or 
branched, which, by the growth of their processes, become connected with one another 
so as to form a network. Their nuclei increase by division : at first these are irre- 
gularly distributed, but, through the growth of the cell-substance, become gradually 
shifted into more or less uniform distances, so that when through the appearance and 
confluence of vacuoles these solid protoplasmic cells and their processes are converted 
into hollow tubes, we find them (viz. the nuclei) more or less regularly distributed in the 
wall of the latter. There is also another mode of development of the first vessels 
in the embryo : this is in isolated cells, at first spherical, and containing one or more 
nuclei— some of them are large multinuclear giant cells— which through vacuolation are 
transformed into vesicles ; these become gradually connected with one another by pro- 
toplasmic threadlike sprouts of their wall, and after these latter have become hollowed 
out, a network of vessels is established, which at first are very irregular, containing 
broad sinuous and narrow tubular parts, but in which these inequalities of diameter 
gradually disappear. 

The development of blood-vessels is the same in the embryo and adult, in normal 
and pathological processes. Strieker was the first who described the formation of 
capillary vessels as a process of hollowing out of solid nucleated protoplasmic cells ; then 
Afanasieff, Klein, Balfour and others described it for the embryo chick, Arnold for the 
development of vessels in the inflamed cornea, Klein and Ranvier for the omentum of 
young and adult animals, Klein for the inflamed serous membranes, and especially 
Leboucq, who proved it for the development of vessels in the embryo and adult, under 
various normal and pathological conditions. 

In connection with the development of vessels in the embryo, out of solid 
protoplasmic cells, there is going on at the same time a formation, in their substance, of 
coloured and colourless blood corpuscles, so that the latter lie in the cavity of the 
former (Klein, Balfour, Leboucq). Blood corpuscles are also formed in the substance 



STRUCTURE OF THE HEART , 47 

of connective-tissue cells of the subcutaneous tissue of new-born animals (Schiifer), 
which by vacuolation are being transformed into capillary vessels. 



In those young vessels that are destined to be arterial or venous branches, the 
original endothelial wall is gradually thickened by cells of the surrounding tissue ; these 
give origin to the elastic, muscular, and connective-tissue elements. 

5. The Heart. 

(a) The outer covering of the heart is a serous membrane (the visceral peri- 
cardium), which, like the other serous membranes, is covered on its free surface with an 
endothelium. The membrane itself is a dense connective-tissue membrane, containing 
networks of elastic fibres arranged parallel to the surface. In the deeper or subserous 
part the connective tissue is looser and contains the large vascular and nervous 
branches, and in many instances larger or smaller groups of fat cells. This con- 
nective-tissue forms a continuity with the intermuscular connective tissue, that is, the 
perimysium separating the bundles of muscle fibres of the substance of the heart 
itself. 

(6) The substance proper of the heart is composed of muscle-bundles, the elements 
of which are striated muscle fibres forming a network and possessing a peculiar struc- 
ture, described and figured on a former occasion (Chapter XI. pp. 78 and 79). The 
bundles are separated by a vascular connective tissue of the nature of ordinary inter- 
muscular connective tissue. In the ventricles they form more or less distinct lamellae. 
The connective tissue separating these lamellae includes oblong clefts (Henle), which 
possess a complete endothelial lining (Schweigger-Seidel), and are therefore to be 
regarded as belonging to the lymphatic system. 

(c) The inner or lining membrane, the endocardium, is covered with a single layer 
of endothelium, which, as has been mentioned in Chapter III., is occasionally in young 
hearts, in some places, as mitral valves, chordae tendineae, and papillary muscles, com- 
posed of germinating cells. Next the endothelium is a delicate membrane, consisting of 
an inner subendothelial network of flat branched cells, and an outer dense network of 
elastic fibrils ; next this follows the chief layer, viz. a connective-tissue membrane, 
composed of bundles of fibrous-connective tissue, arranged as small trabecular, running 
in different directions and crossing each other under various angles ; between them 
lie the ordinary connective-tissue corpuscles in the interfascicular lymph spaces, and 
also numerous networks of elastic fibres. 

The deep parts are made up of connective-tissue bundles, which further on pass as 



A A 2 



i 4 8 ATLAS OF HISTOLOGY. 

perimysium between the muscle bundles of the heart's substance. The thickness of the 
endocardium varies in different localities; at the ostium of the auricles and ventricles and 
the summit of the papillary muscles it is greatly increased by a firm connective tissue, 
identical with tendinous tissue and situated underneath the proper endocardial membrane. 
The same firm tendinous tissue occupies the middle layer of the auriculo-ventricular 
valves which represent merely folds of the endocardial membrane. The semilunar valves 
are also folds of the endocardium, but contain chiefly elastic tissue. Striated muscle 
fibres penetrate a short distance into the auriculo-ventricular valves ; they are longitu- 
dinal and transverse bundles, and are continuations of the muscles of the auricle 
(Joseph, Gussenbauer). The endocardium of the septum ventriculorum of man 
contains small bundles of unstriped muscle fibres (Schweigger-Seidel). 

In the subendocardial tissue are tracts of striped muscle fibres which differ in no 
way from those of the hearts substance ; they belong to the endocardium, since they are 
separated from the proper substance of the heart by special layers of connective tissue 
(Schweigger-Seidel). Amongst the muscle fibres of the endocardium are Purkinjes fibres 
specially to be mentioned. They form a network. They do not occur in man, rabbit, 
mouse, cat, and frog (Aeby, Obermeyer), but are met with in many other mammals 
and birds (Purkinje, Kolliker, Aeby, Lehnert, Obermeyer and others). Each of them 
represents a thin muscle fibre, the central part of which is homogeneous protoplasm, 
containing nuclei at regular intervals, while its periphery is striated muscle substance 
(Schweigger-Seidel, Frisch). 

The networks of blood capillaries are of course richest in the muscle substance, but 
they are also numerous in the pericardial and endocardial membrane, including the 
valves. 

The lymphatic vessels form a pericardial and an endocardial network ; into this 
latter pass the lymphatics of the mitral as well as of the semilunar valves (Eberth, 
Belajeff). The individual vessels are comparable to lymphatic capillaries (see a future 
chapter). The muscle substance proper of the heart possesses, besides the above-named 
lymph spaces of Schweigger-Seidel, also other tubular lymphatics (Lusckka, Eberth, 
Belajeff). 

The nerve branches of the plexus cardiacus, those that run as subpericardial nerves 
towards the apex of the heart, as well as those situated in the septum ventriculorum, 
form plexuses ; each branch represents a small bundle of ordinary non-medullated nerve 
fibres, held together by a perineural sheath : amongst them may be met with here and 
there a medullated nerve fibre. 

In connection with the nerve plexus of certain places, to be mentioned presently, are 



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GANGLIA OF THE HEART. , 49 

minute ganglia ; they vary in size and bear the same relation to the nerve branches as 
the microscopic sympathetic ganglia described in Chapter XVII. B. } being smaller or 
larger spherical, spindle-shaped or irregular groups or chains of ganglion cells. 

The ganglia are very conspicuous in the nerve plexus of the septum auriculorum of 
the heart of frog (Ludwig, Bidder, and others), also in the septum between auricle and 
ventricle of the same animal (Dogiel). The ganglion cells in the frog's heart are, 
according to Beale, possessed of a 'spiral fibre,' but this is denied by Dogiel. 

In man and mammals ganglia are present in connection with the subpericardial 
nerve branches (Schklarevski, Dogiel). According to Dogiel they lie chiefly at the point 
where the large veins enter the heart, and at the boundary between the auricles and the 
ventricles. There are no ganglia in other parts of the heart of man and mammals, as 
maintained by Remak and others. The ganglion cells arc of various sizes ; most of them 
are possessed of one process only, which is an axis-cylinder process. Their structure 
and relation to nerve fibres is the same as that described of the sympathetic ganglion 
cells of man and mammals in Chapter XVII. B, 

PLATE XXVI. 

Figs. I. IV. V. VIII. and IX. are drawn under a magnifying power of about 350 ; 
the rest under one of about 250. 

Fig. I. Part of a transverse section through the ascending aorta of pig. The 
figure represents about the inner fourth of the whole thickness of the wall. 

a. Lining endothelium ; the nuclei of its cells are shown only. 

b. Subendothelial layer of connective tissue, showing in a homogeneous matrix 
oval nuclei of connective-tissue corpuscles and numerous dots, being longitudinal con- 
nective-tissue fibres viewed in transverse section. 

c. and d. represent the inner coat proper or intima, composed of elastic tissue ; at c. 
most of its fibrils run circularly ; at d. the substance is represented homogeneous, with 
only few elastic fibrils (dots) in transverse section, but there is in reality a dense net- 
work of such fibrils. 

e. Inner portion of the middle coat or media. It contains in a matrix of very fine 
elastic fibrils, represented here as a homogeneous purple ground-substance, thick bright 
cylindrical elastic fibres, which, being arranged longitudinally, are here seen in trans- 
verse section; in some places they are more or less coalescing, so as to form mem- 
branous structures ; besides the elastic fibres are unstriped muscle cells, which., being 
placed more or less longitudinally, are represented here transversely or obliquely. 

/ Beginning with this part the thick elastic fibres of the previous layer form by 



i 5 o ATLAS OF HISTOLOGY. 

confluence elastic membranes separating the unstripecl muscle cells ; these have become 
arranged transversely. 

Fig. II. Lower part of a minute artery viewed in longitudinal (optical) section ; c. 
to a. represents the thickness of the wall seen in profile. 

e. Nucleated endothelial membrane, lining the lumen of the vessel, seen in profile. 
In the lumen appear several faint oval nuclei ; these are the nuclei of the endothelium 
looked at from above. 

i. Very thin elastic intima. 

vt. Muscle coat or media ; the unstriped muscle cells, being arranged circularly, are 
here seen as if cut transversely. 

a. Nucleated membrane representing the adventitia. 

Fig. III. Transverse section through the carotis of dog. 

e. Lining endothelial membrane seen in profile. 

i. Elastic intima. The subendothelial connective-tissue layer is too delicate to be 
seen in a transverse section. 

m. Media, containing bright wavy elastic membranes, viewed here in profile, 
separating the circular bundles of unstriped muscle cells, of which only the staff- 
shaped nuclei are here shown. The networks of fine elastic fibrils, passing from one 
elastic membrane to another, are not represented here. 

a. Adventitia, consisting of bundles of connective tissue indicated by a yellowish- 
brown tint ; between the bundles are seen the deeply stained nuclei of connective-tissue 
corpuscles and bright cylindrical elastic fibres which, running longitudinally, are here 
represented in transverse section. Their number is greatest towards the media. 

Between the adventitia and media is a wavy elastic membrane, Henle's elastica 
externa. 

Fig. IV. Transverse section through a large branch of the inferior mesenteric 

artery of pig. 

e. Endothelial membrane. 

i. Elastic intima. The subendothelial connective-tissue layer being exceedingly 
thin, is not seen. 

m. Muscular media, containing only a few of the bright wavy elastic membranes ; 
the network of fine fibrils separating the bundles of muscle cells are not represented. 

A distinct elastica externa divides the media from the connective-tissue adventitial, 
which has the same structure as that in the previous figure. 

Fig. V. Transverse section through a small artery and vein of the mucous mem- 
brane of the epiglottis of a child. 

A. Artery, showing the lining nucleated endothelium ; the vessel being contracted, 



STRUCTURE OF BLOOD-VESSELS. l$l 

the endothelial cells appear very thick. Underneath the endothelium is the wavy 
elastic intima. The chief part of the wall of the vessel is occupied by the circular 
muscle coat ; the staff-shaped nuclei of the muscle cells are well seen. Outside this is- 

a. Part of the adventitia ; this is composed of bundles of connective-tissue fibres, 
shown in section, with the nuclei of the connective-tissue corpuscles. The adventitia 
gradually merges into the surrounding connective tissue. 

v. Vein, showing a thin endothelial membrane raised (accidentally) from the inti.ua 
which, on account of its delicacy, is seen as a mere line on the media ; this latter is 
deeply stained and composed of a few circular unstriped muscle cells. 

a. The adventitia is similar in structure to that of the artery. 

Fig. VI. Surface view of the endothelium lining a large vein of the frog's 
mesentery, stained with nitrate of silver. The outlines, i.e. the interstitial cement-sub- 
stance, of the endothelial cells is shown only, not their nuclei. Underneath the endo- 
thelium are seen a few of the outlines of the circular muscle cells. 

Fig. VII. Surface view of a minute artery from a silver-stained omentum of 
rabbit, showing the outlines of the elongated endothelial cells lining the vessel ; at the 
margin of the vessel are seen the outlines, i.e. the interstitial cement-substance, of the 
circular muscle cells. 

Fig. VIII. Part of a capillary artery of the omentum of dog, seen lengthwise. The 
lining endothelium is seen in profile at the margin, the oval nuclei seen apparently in 
the vessel are the nuclei of the endothelium viewed from the surface. The nuclei of the 
endothelial cells, being flattened like the cells themselves, appear broader when seen 
from the surface than in profile. 

The media is indicated by groups of circular muscle cells arranged alternately. 
An outer delicate nucleated membrane represents the adventitia. 

Fig. IX. Transverse section through a large branch of the mesenteric vein, accom- 
panying the artery represented in Fig. IV. 

e. The lining endothelium, its nuclei are well shown. 
i. Delicate elastic intima. 

m. Media, the inner part of it is a continuous circular layer of unstriped muscle 
cells, but the outer greater portion contains muscle cells arranged only in small 
bundles, and separated by a great amount of connective tissue, with a few thick elastic- 
fibres. 

a. Adventitia of connective tissue, with numerous thick cylindrical longitudinal 
elastic fibres, similar to those in the adventitia of the artery. 

The difference in the relation of the various coats and their relative and absolute 
thickness in the two vessels, represented in Figs. IV. and IX., is well marked. 



152 ATLAS OF HISTOLOGY. 



PLATE XXVII. 



All figures, except Fig. XVI., are drawn under a magnifying power of about 350 ; 
fig. XVI. with one of about 100. 

Fig. X. From an omentum, stained with nitrate of silver, of rabbit. 
v. Capillary vein ; the nucleated endothelial cells lining the vessel are well shown. 
a. Young sprouts connected with branched connective-tissue cells ; 
c. Unfinished capillaries, viz. such as are in the process of being hollowed out, and 
whose wall has not yet become differentiated into endothelial cells. 

There are other rudiments of capillaries, but they are still solid protoplasmic 
threads. 

Fig. XL A branched capillary vessel from the frog's bladder, stained with chloride 
of gold ; only the nuclei of the endothelial wall are shown, the preparation, not having 
been stained in silver, does not show the outlines of the individual endothelial cells. 
A distinct intranuclear network is seen in each nucleus. There are several coloured 
blood corpuscles, stained by the gold, in the lumen of the vessel. In the surrounding 
tissue are seen the branched connective-tissue cells. 
m. Migratory cells. 

Figs. XII. and XIV. represent capillary vessels of the frog's mesentery, stained 
with nitrate of silver only; the wall of the vessel is viewed from the surface, and is seen 
to consist of elongated endothelial plates, marked by their outlines only ; the nucleus of 
the individual endothelial cells is not shown. 

Fig. XIII. Young capillaries of the omentum of guinea-pig. 

v. Young capillary vein, showing the nuclei of the endothelial wall. The rest is a 
network of developing capillaries, which, in several places, are still in the stage of solid 
protoplasm ; in all of them are transverse septa, being the remnants of the proto- 
plasm separating the vacuoles. 

Fig. XV. Developing capillaries from the tail of tadpole, stained first in chloride 
of gold and then in haematoxylin. 

v. Capillary vein, clumps of pigment in its wall. 

a. Solid nucleated protoplasmic sprout of the capillary wall meant to become 
hollowed out. 

b. Thin threads of solid protoplasm connecting the wall of two capillaries. These 
threads are evidently the processes by which the two cells, now transformed into the 
right and left capillary, were originally connected with one another ; when hollowed out 
such connecting threads represent the branches through which two vessels anastomose. 



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DEVELOPMENT OF CAPILLARIES. 153 

The small oval nuclei belong to the wall of the vessels. There are four oval 
nucleated granular corpuscles in the right vessel ; they are young coloured blood- 
corpuscles. 

Fig. XVI. Surface view of an artery ensheathed ill a perivascular lymphatic 
vessel, from the frogs mesentery, stained with nitrate of silver. 

a. The artery ; its deeply-stained circular muscle coat (media) is indicated by 
broad transverse markings ; outside it is an indication of a lighter stained adventitia. 

/. Lymphatic vessel ; its wall is a simple endothelial membrane. 

Fig. XVII. From the same preparation as Fig. XV. 

a. Nucleated protoplasmic cell connected with the wall of a capillary vessel. 

c. Nuclei of the wall of the capillary vessel. Two coloured blood-corpuscles in the 
middle part of the figure. 

The vessel represented here still recalls the branched cell from which it has 
developed, several of its processes, like the body of the cell, having become hollowed out ; 
two processes are still solid, and a third one is connected with a spindle-shaped looking 
protoplasmic corpuscle, a, of the surrounding tissue. 



B B 



i S4 ATLAS OF HISTOLOGY. 



CHAPTER XX. 

LYMPHATIC GLANDS. 

A. Compound Lymphatic Glands. 

As such are to be regarded the glands that are interposed in the course of 
lymphatic trunks, as the subcutaneous lymphatic glands, the cervical glands, the 
bronchial and mesenteric glands, the glands at the hilus of the spleen and liver, &c. 
The knowledge of their structure we owe chiefly to the researches of Kolliker, Frey, 
and Teichmann, and especially His and v. Recklinghausen. Each gland consists of: 
(i) a framework, (2) the gland tissue proper, (3) the lymphatics, and (4) the blood-vessels 
and nerves. 

(1) The framework is composed of : (a) the capsule, a connective-tissue mem- 
brane arranged as an outer and inner stratum. The former is composed of bundles 
of fibrous-connective tissue crossing each other in different directions; between the 
bundles are the ordinary connective-tissue corpuscles ; a limited number of elastic 
fibrils connected into a network may be always met with, and also occasionally groups 
of fat-cells. This outer stratum is connected with the surrounding loose connective 
tissue. The inner stratum shows a lamellar structure ; the lamellae consist of parallel 
bundles of fibrous connective tissue, and are separated from each other by flat connec- 
tive-tissue corpuscles. Migratory cells may be occasionally met with between the lamellae. 
(6) In connection with this inner stratum are membranous septa, which penetrate 
into the interior of the gland in a direction vertical to the surface but more or less 
radiating towards the hilus, from which emerge the efferent lymphatics. These septa 
are of the same structure as the inner stratum of the capsule, of which they are direct 
prolongations. 

(c) Having penetrated into the gland for a considerable distance, varying 
in different glands and even in different parts of the same gland, the septa 
branch into broader or narrower trabecule, which run in all different directions and 
anastomosing with one another form plexuses with relatively small meshes. The 
structure of the trabecular is the same as that of the septa. The part of the gland 
containing the septa is spoken of as the cortex, the rest, viz. that containing the plexuses 
of the trabecule, as the medulla. 



STRUCTURE OF COMPOUND LYMPHATIC GLANDS. 155 

The cortex is subdivided by the septa into a single stratum of longer or shorter 
oval compartments. Owing to the former (septa) possessing a more or less radiating 
direction, most of the latter (compartments) are broader at their capsular surface than 
towards the medulla. 

The septa between two neighbouring compartments not being complete, these 
latter communicate with one another laterally. Towards the medulla the compartments 
are in open communication with the spaces pertaining to the medulla, viz. those con- 
tained in the plexuses of the trabecule. In many mammals (Heyfelder), especially 
pig and calf, the septa and trabecule contain unstriped muscle-cells, some of the 
trabecular being almost entirely muscular. 

Besides the flat connective-tissue corpuscles, the septa and the trabecular contain in 
some instances (pig, guinea-pig, occasionally also man) numerous plasma-cells of Waldeyer. 

It is essential for the understanding of the structure of the compound lymphatic glands to 
have a clear conception of the arrangement of the framework. In examining sections through 
these glands it is necessary to be aware that only those sections that pass through the gland in 
the direction of the septa, show the exact relations of the cortex and medulla, and the shape and 
size of the above compartments. 

(2) The gland tissue proper ox adenoid tissue (His) occupies the above compart- 
ments of the cortex and the spaces between the trabecular of the medulla. From the 
peculiar arrangement of the framework as above described it follows that the adenoid 
tissue forms in the cortex a stratum of oval or egg-shaped masses, follicles ; these masses 
pass in the shape of more or less cylindrical tracts, medullary cylinders, into the medulla, 
where they anastomose into a network. The cortical follicles are everywhere separated 
from the capsule and septa by a distinct and almost uniform space, lymph-sinus (I lis) ; 
the same relation exists also in the medulla, the medullary cylinders being separated 
from the trabecular by uniform lymph-sinuses. 

The lymph-sinuses of the cortex represent therefore the peripheral portion of the 
above compartments, and their boundaries are consequently the outer surface of the 
follicles on the one hand, and the inner surface of the capsule and septa on the 
other ; the lymph-sinuses of the medulla are the spaces between the surface of the 
medullary cylinders and the trabecular. From what has been said above, on tin- 
occasion of the framework, the cortical sinuses intercommunicate with one another ; so 
do, of course, the medullary sinuses; and also the former are in open communication 
with the latter. 

The structure of the adenoid tissue both in the follicles of the cortex and in the 
cylinders of the medulla is precisely the same ; it is this : (a) the ground substance or 
matrix is a dense reticulum, adenoid reticulum, of fine homogeneous fibrils and mem 



B B 2 



156 ATLAS OF HISTOLOGY. 

branes joined into a honeycomb. This honeycomb contains all gradations between 
fibrils and plate-like expansions. Its chemical nature is not definitely ascertained ; it is 
neither identical with elastic tissue nor with common fibrous tissue. 

(b) Applied to this adenoid reticulum are from place to place transparent flattened 
(connective-tissue) endot keloid cells, each with an oval but flattened nucleus. The large 
clear nuclei, which in an ordinary section are situated appare7itly in the nodes of the 
reticulum, are in reality the nuclei of these endotheloid cells fixed on the reticulum. 
By prolonged shaking or pencilling of a section of the gland all the endotheloid cells 
can be removed from the reticulum, and this latter is then seen to be barren of any 
nuclei, at any rate in the adult state (Bizzozero, Klein). In embryonal life and during 
early periods of development the reticulum, being derived from branched cells, possesses 
nuclei, but these disappear as the development advances. 

(c) The meshes of the adenoid reticulum contain, according to their size, two, three 
or more lymph-corpuscles ; they are completely filled by the latter. These lymph- 
corpuscles are small cells, each with a conspicuous spherical nucleus, staining deeply in 
ordinary dyes. In most corpuscles the amount of cell-protoplasm surrounding the nucleus 
is very small and escapes superficial observation. An ordinary section through adenoid 
tissue reveals at first sight only these nuclei, densely crowded ; of the delicate cell- 
substance surrounding each of them, and of the adenoid reticulum containing them, very 
little is to be noticed. The nucleus of the lymph-corpuscles is smaller than that of the 
endotheloid plates, spherical, whereas the nucleus of the latter is oval and flattened, 
and stains more deeply and appears therefore less transparent than the latter. The 
intranuclear network is always more distinct in the latter than in the former. When 
carefully examining the lymph-corpuscles it will be seen that some of them are larger 
than others, possessing a larger amount of cell-protoplasm ; they contain one or two 
nuclei, and are considered in a more advanced state of development ; under suitable 
conditions they show amoeboid movement. They differ from ordinary colourless blood- 
corpuscles chiefly in the fact that the nuclei are larger in the former than in the latter. 

(d) The adenoid tissue is richly supplied with blood-vessels ; like all glandular 
tissues, it contains a dense network of capillaries. These differ from ordinary capillaries 
in so far as they obtain from the adenoid reticulum a special sheath, the capillary 
adventitia (His). 

The adenoid tissue occurs also in the simple lymphatic glands and other kindred 
organs ; it possesses everywhere the same structure, and we shall, therefore, not detail its 
structure again, when describing the latter. 

(3) The lymphatics ; the afferent lymphatics enter the capsule and branch here into 



LYMPH SINUSES OF LYMPHATIC GLANDS i 57 

numerous vessels which are connected into a dense network ; the vessels of this network 
are situated in the outer stratum and between this and the inner stratum. They are 
lymphatic tubes with valves and corresponding saccular dilatations. From this network 
vessels pass into the depth and open into the cortical sinuses. As has been mentioned 
above, these are freely connected with the medullary sinuses forming an intercom- 
municating system. At the hilus tubular lymphatics are developed from the medullary 
sinuses. Some of these vessels may be traced, embedded in a trabecula, for a considerable 
distance into the medulla of the gland. They are possessed of valves and corre- 
sponding saccular dilatations ; at and near the hilus they are connected into a net- 
work. From this network are developed the efferent lymphatic trunks. 

The stream of lymph or injection fluid passing through the gland is therefore 
from the afferent vessels into the capsular network ; from here into the cortical, then 
into the medullary, sinuses ; from these into the network of lymphatics of the hilus, and 
finally into the efferent lymphatic trunks. 

Neither the cortical nor medullary sinuses are, however, free passages like the 
other lymphatics, for they are filled with a spongy substance, a peculiar reticulum, by 
which their cavity is subdivided into minute spaces. 

This reticulum, although in some respects similar to the adenoid reticulum, 
differs from the latter by being thicker and coarser, and its meshes larger. Like the 
adenoid reticulum it is also of a homogeneous nature. We have, then, a sponge-like 
reticulum occupying the sinuses that separate, in the cortex, the surface of the 
follicles from the inner stratum of the capsule and septa, and in the medulla, the surface 
of the lymphatic cylinders from that of the trabecular 

The afferent lymphatics, those of the capsular network, as well as the lymphatics of 
the hilus and the efferent trunks, are lined with a single layer of endothelium like other 
lymphatics to be specially described in one of the next chapters, so are also the sinuses 
of the cortex and medulla : both the surface of the follicles and of the medullary 
cylinders, on the one hand, and that of the septa and trabecula-, on the other, being 
covered with a layer of endothelial cells. 

This endothelium is continuous on to the aforesaid spongy reticulum, stretching 
through the sinuses ; the flattened endothelial cells do not, however, cover the spaces oi 
the reticulum, but keep close to its fibres and membranes. 

In some animals (bovine) the endothelial cells of the sinuses of the medulla, both 
those covering the medullary cylinders and trabecular as well as those belonging to the 
spongy reticulum, are filled with yellowish-brown pigment granules; hence the medulla 
presents already in the fresh state a dark brown colour. 

The meshes of the reticulum of the cortical and medullary sinuses generally contain 



158 ATLAS OF HISTOLOGY. 

numerous lymph-corpuscles ; the greater majority of these possess a well-marked 
cell-protoplasm surrounding the relatively large nucleus, and are therefore to be considered 
as in a ripe state. Passing a current of fluid through the afferent lymphatics of the gland, it 
will be found that these lymph-corpuscles are readily removed from the cortical and 
medullary sinuses into the efferent lymphatics, and there is no reason why the 
similar thing should not happen already during life. It is supposed that these 
lymph-corpuscles are produced in the follicles and medullary cylinders, whence 
they are floated into the lymph-sinuses by the natural current of plasma passing 
from the capillary blood-vessels towards the lymphatics (Recklinghausen), similar 
to what is the case in all other tissues (see a future chapter). In this the lymph - 
corpuscles are very probably aided by their amoeboid movements. After having 
been discharged by the lymphatics into the venous system they represent colourless 
blood-corpuscles. 

(4) The blood-vessels and nerves. The arterial and venous branches are 
embedded in the trabeculae and septa, the networks of capillaries, including capillary 
arteries and veins, belong entirely to the adenoid tissue. The distribution of fine nerves 
is not known. 



B. Simple Lymphatic Glands. 



As such are to be considered the masses of adenoid tissue occurring in the shape 
of spherical or oval lymph-follicles, singly or in groups, or as nodular and cord-like, or 
irregularly defined accumulations. 

The tonsils are folds of the oral mucous membrane containing a collection of lymph- 
follicles. The surface, like that of other parts of the mucous membrane of the oral cavity, 
is covered with stratified pavement epithelium ; underneath this is a connective-tissue 
mucosa, which contains closely aggregated spherical or oval lymph-follicles. In adults 
the number of them is very great and the mucosa is so much folded, that hereby numerous 
pit- or cleft-like depressions become apparent on its surface. Towards the epithelium of 
the surface the adenoid tissue of the follicles is more or less diffuse, penetrating in many- 
places into the epithelium itself; here the epithelial cells give way before the ade- 
noid reticulum and the lymph-corpuscles. 

At the root of the tongue (Kolliker, Huxley) and in the upper part of the pharynx 
(Kolliker, Luschka) a similar accumulation of lymph-follicles is met with. 

The thymus gland is an aggregation of well-defined more or less cylindrical masses 
of adenoid tissue anastomosing into a network ; these masses are separated from each 



SIMPLE LYMPHATIC GLANDS. I59 

other by fibrous connective tissue, which together with the capsule form the framework 
of the gland. This will be described more minutely in the next chapter. 

Similar lymph-follicles, singly or in groups, or as diffuse masses of adenoid tissue, 
occur in the mucous membrane covering the posterior surface of the epiglottis, in the 
walls of the ventriculus Morgagni of the larynx, and in the conjunctiva. The mucosa 
of the pyloric end of the stomach possesses lymph-follicles, either singly or in groups, as 
the so-called glandulae lenticulares. 

The small intestine contains lymph-follicles, either singly as solitary, or in smaller 
or larger groups, as agminated glands. In both cases they are situated with their chief 
portion, viz. the body of the follicles, in the submucous tissue ; with the rest they are 
pushed through the muscularis mucosae into the mucosa. In the agminated glands each 
individual follicle reaches the inner free surface of the intestine, and like this is covered 
with columnar epithelium. This end represents the summit, the opposite the basis of 
the follicle. The epithelium, covering the summit of the follicles, is in many parts 
altered by the growth of the subjacent adenoid tissue into it, the individual epithelial 
cells giving way before the growing reticulum and lymph-corpuscles (Watney). In 
consequence of the above arrangement of the follicles of the agminated glands, the 
mucosa, containing Lieberkiihn's crypts, and covered with villi, is reduced to minute 
folds between the summits of the follicles. The mucous membrane appears at the same 
time much thicker than the surrounding parts, and is conspicuous as a patch somewhat 
projecting over the general surface. Such a patch is called a Peyer's patch. In the 
Peyer's patches the follicles are arranged in a single stratum, and are confluent witli 
their middle portion, but separate at the summit and basis. The number of follicles 
contained in a Peyer's patch varies greatly, and hence also the size of the latter. 
Their numbers and sizes increase towards the ileo-caxal valve ; in carnivorous animals 
the mucous membrane of the lower part of the ileum is one single large Peyer's 
patch. 

In the large intestine we meet with single lymph-follicles which are considerably 
larger than the solitary glands of the small intestine; they are also situated with 
their body in the submucous tissue ; occasionally they are pushed through the muscu- 
laris mucosae and penetrate into the mucosa. In the rabbit the mucous membrane of 
the caecum is filled with lymph-follicles, which possess the same relation to one another 
and to the mucosa as those in the Peyer's patches : in fact, the mucous membrane is a 
Peyer's patch with the difference that there are no villi. 

The adenoid tissue of the lymph-follicles of the small and large intestine passes at the 
sides below their (follicles) summits, directly into the tissue of the mucosa, both being in 
all respects similar in structure. 



160 ATLAS OF HISTOLOGY. 

The mucous membrane of the small bronchi contain isolated lymph-follicles, and 
also diffuse masses of adenoid tissue. 

The spleen contains cylindrical masses of adenoid tissue ensheathing the arterial 
branches ; these cord-like masses are possessed of oval or spherical enlargements, either 
uniform or one-sided. The Malpighian corpuscles of the spleen, generally incorrectly 
represented as spherical or oval bodies placed laterally on an arterial branch, are, in the 
majority of instances, transverse sections through such a cord-like mass of adenoid 
tissue ensheathing an artery ; this vessel is generally situated excentrically, being sur- 
rounded by a greater amount of the adenoid tissue on one side than on the other. 

The serous membranes (omentum, pleura mediastini) contain smaller or larger 
nodular, patch-like, or cord-like masses of adenoid tissue, covered on one or both 
surfaces with germinating endothelium, as has been mentioned in Chapter III. (p. 21). 
These masses have either a well-defined outline, or they are more or less diffuse ; their 
growth and relation to fat-tissue has been referred to in Chapter VI. (pp. 42 and 43). 

Smaller or larger diffuse masses of adenoid tissue occur occasionally in the mucous 
membrane of the false vocal cords and trachea, in the mucosa of the soft palate and uvula, 
in the oesophagus, in the tissue in which the tubes of the epididymis are embedded, and 
in the interlobular tissue of the pancreas. 

The adenoid tissue contains in its adult state a special system of blood-vessels. 
This is especially the case in the follicles, both single and in groups ; each follicle 
contains an afferent arterial branch, one or more venous branches, and an intermediary 
network of capillaries. In the follicles of the root of the tongue, in those constituting 
the tonsils, in those of the upper part of the pharynx, in the solitary follicles of the 
small and large intestine, and in those of the Peyer's patches, the veins form a plexus 
around the follicles, while the capillaries are arranged more or less radiating towards 
the centre of each follicle. The number of capillaries in a follicle is generally consider- 
able, but there are differences in this respect in different organs : thus, the follicles of 
the intestine are much richer in capillary vessels than the follicles of the tonsils, or the 
Malpighian corpuscles of the spleen. 

The follicles of the root of the tongue, tonsils, pharynx, intestine, bronchi, &c, are 
surrounded, over a larger or smaller portion of their circumference, by a lymph-sinus 
(His, Frey, and others), which is in open connection with a lymphatic vessel of the 
surrounding tissue. Both the visceral surface, i.e. that belonging to the follicle, as well 
as the parietal surface, i.e. that separating the sinus from the surrounding connective 
tissue, is covered with a layer of endothelial plates with more or less sinuous outlines. 



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DEVELOPMENT OF LYMPHATIC FOLLICLES. 161 

The lymph-follicles develop as masses of adenoid tissue around the wall of a 
lymphatic, generally unilaterally (Klein). So that they are from the outset surrounded 
on one side by a lymph-sinus, this being part of the lymphatic vessel. In many in- 
stances the first appearance of the adenoid tissue is in the wall of a small arterial 
branch between this and a neighbouring lymphatic. 

Also the compound lymphatics have a similar history, inasmuch as Sertoli has 
shown that they are developed as masses of adenoid tissue in the wall of lymphatics 
connected into a network. 

Sometimes even in adults (subcutaneous tissue of guinea-pigs and rabbits), small 
compound lymphatic glands may be seen developing as masses of adenoid tissue with 
its capillary blood-vessels in the sheath of a minute artery ; these masses form cylinders 
and are connected into a network, surrounded by, and embedded in, a network of lym- 
phatics. These cylinders become very much enlarged at the periphery as cortical 
follicles. In the cavity of the lymphatics, viz. the future sinuses, a young reticulum 
makes its appearance later on. 

PLATE XXVIII. 

Fig. I. From a vertical section through a compound lymphatic gland of dog, the 
afferent lymphatics of which had been injected with Berlin blue. The section had 
been stained in picrocarmine. Magnifying power about 25. 

c. Capsule, containing a few lymphatics cut transversely, these open into the 
cortical sinuses. 

a. Lymph-follicles of the cortex, surrounded by lymph-sinuses. 

b. Medulla, showing the network of (pink) cylinders of adenoid tissue, and the 
lymph-sinuses injected blue ; the injection-matter appears in the form of a network 
owing to its being deposited on the reticulum contained in these sinuses. The trabecule 
are not visible under this low power. 

Fig. II. A portion of the medulla of the same gland as represented in the 
previous figure, somewhat more magnified, about 90. The section had been stain. « I, 
first in picrocarmine, and then in hematoxylin. 

a. Trabecular of various sizes. 

b. Medullary cylinders, cut in different ways ; their minute structure is not shown. 

c. Lymph-sinuses, showing the injection-matter deposited as a network. 

Fig. III. From a vertical section through the capsule, cortical sinus, and 
peripheral portion of follicle of a human compound lymphatic gland. The section had 
been shaken, so as to get rid of most lymph corpuscles. Magnifying power about 350. 

c c 



1 62 ATLAS OF HISTOLOGY. 

c. Capsule composed of an outer and inner stratum. The former consists of bundles 
of fibrous connective tissue cut in various ways, because running in different directions ; 
the latter possesses lamellae of connective tissue with flattened connective-tissue cor- 
puscles between ; only the nuclei of the latter are shown. 

s. Lymph-sinus, containing a reticulum and on it nucleated flattened endothelial cells. 

a. Adenoid tissue of lymph-follicle, shaken. The surface of the follicle is covered 
with a distinct nucleated membrane, endothelium. Numerous nuclei, indicative of 
lymph-corpuscles, are left in the adenoid reticulum. 

Fig. IVa. Shaken adenoid tissue of cortical follicle of a mesenteric gland of calf. 
The adenoid reticulum, a, is well seen ; only few nuclei of lymph-corpuscles are left in its 
meshes. The oval nuclei are indicative of the hyaline flattened endothelial cells ; c is a 
capillary blood-vessel ensheathed in the adenoid reticulum. Magnifying power about 300. 

Fig. IVb. Part of a Malpighian corpuscle of spleen of man. Magnifying power 
about 350. 

a. Arterial branch in longitudinal section. 

b. Adenoid tissue, still containing the lymph-corpuscles; only their nuclei are shown. 

c. Adenoid reticulum ; the lymph-corpuscles had been removed accidentally. 

Fig. V. From a section through the medulla of a rabbit's mesenteric gland, the 
lymphatics of which had been injected with nitrate of silver. Magnifying power 
about 350. 

a. Trabecula ; at ^it is seen from the surface, and therefore it appears covered with 
an endothelium ; the rest of the trabecula, being cut longitudinally, shows only at the 
margin the endothelium in the form of a thin dark line. 

This endothelium is seen in many places, especially towards the lower part of the 
figure, to extend on the reticulum occupying the lymph sinuses, c ; the nuclei on the 
reticulum correspond to these endothelial plates. 

b. Medullary cylinders ; except the nuclei of the lymph-corpuscles, their structure is 
not shown. 

Fig. VI. From a section through the medulla of a mesenteric gland of ox. Mag- 
nifying power about 300. 

a. Trabecular 

b. Medullary cylinders; their minute structure, except the nuclei of the lymph- 
corpuscles, is not represented. 

c. The reticulum occupying the lymph-sinuses ; this reticulum is covered with 
nucleated flat endothelial cells containing brown pigment granules. Both the surface of 
the trabecular and medullary cylinders are seen to be covered with the same endothelial 
cells shown in profile. 



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LYMPHATIC GLANDS. 163 



PLATE XXIX. 

Fig. VII. From a vertical section through the skin of pigs ear-lobe, to show the 
distribution of the lymphatics. This figure is illustrative of a point to be considered in 
the chapter on lymphatic vessels. 

b. Distended blood-vessels in transverse section. 

I Lymphatic vessels, their wall a single layer of endothelial plates ; these vessels 
are in open communication with the lymph-canalicular system, the intercommunicating 
interfascicular spaces ; they contain the nucleated connective-tissue corpuscles, seen here 
in profile. 

The skin had been cedematous, and hence all the interfascicular spaces are abnor- 
mally distended, as shown at c. 

The blood-vessels are also surrounded by these lymph spaces. 

The connective-tissue bundles cross each other in different ways and are therefore 
cut in various directions, most of them transversely and obliquely. 

Fig. VIII. From a vertical section through a mesenteric gland of rabbit. Magnify- 
ing power about 100. 

a. Peripheral portion of cortical lymph-follicles ; under this power they appear as 
a dense accumulation of nuclei. 

s. Lymph-sinus ; the lymph-corpuscles have been removed. 

c. Inner stratum of capsule. 

/. Septa coming off from the capsule, and passing in between the follicles. 
Fig. IX. From the same preparation as in the preceding figure, but illustrating the 
portion of the medulla adjoining the cortex. 

a. Transition of the cortical follicles into the medullary cylinders. 

b. Lymph-sinuses ; the lymph-corpuscles, with which they are ordinarily filled, have 
been removed by shaking. 

c. Trabecular. 

d. Medullary cylinders of adenoid tissue ; their minute structure is not to be made 
out under this low power, and they appear merely as a collection of nuclei. 

Fig. X. Vertical section through a Peyers patch of caecum of rabbit, showing two 
lymph-follicles and their relation to the other parts of the wall of the intestine. Mag- 
nifying power about 100. 

a. Middle part of lymph-follicles, i.e. the part where they are fused. 

s. Summit of follicles covered by the epithelium of the surface ; the adenoid tissue 



l64 ATLAS OF HISTOLOGY. 

of the follicle penetrates, as a rule, in many places into this epithelium ; but this point is 

not represented in the figure. 

m. Mucosa pressed into folds, and containing the crypts of Lieberkiihn, most of 

them being cut transversely. 

The basis of the follicles is surrounded by lymph-sinuses separated from each other 
by the connective tissue of the submucous tissue, containing the large blood-vessels and 

lymphatics. 

c. External circular muscular coat. 

b. External longitudinal muscular coat, cut transversely. 

/. Peritoneal covering, separated from the muscular coat by the subserous lym- 
phatics. 

Fig. XL A portion of dog's pleura mediastini, stained with nitrate of silver. 

Magnifying power about ioo. 

a. Fenestrated membrane, its trabecular are covered with flattened endothelium. 

b. Large trabecular, more or less freely projecting over the general surface. 

c. Nodular masses composed of adenoid tissue and covered with germinating 

endothelium. 

b and c contain numerous amorphous black particles, which are carbon particles. 
The lymphatics of both lungs and the bronchial glands of the same animal were also 
filled with carbon. This will be referred to in the chapter on the lymphatic vessels. 

Fig. XII. From a transverse section through a portion of the tonsil of dog. 
Magnifying power about ioo. 

e. Stratified pavement epithelium. 

l. Diffuse adenoid tissue, filling the mucosa and penetrating at the depth of the 
fold, represented in the middle of the figure, into the epithelium of the surface. 

F. More or less well-defined lymph-follicles. 

m. Part of a mucous eland situated in the submucous tissue. 



i65 



CHAPTER XXI. 

THE THYMUS. 
A. The Framework. 

A "capsule of fibrous tissue surrounds the gland; into the interior of the latter pass 
septa connected with the former and carrying the arterial and venous branches and tin- 
efferent lymphatics. The large septa branch into smaller ones ; by the former the -land 
is subdivided into lobes, by the latter into lobules. Lamella? of connective tissue, derived 
from the interlobular septa, pass into the individual lobules, and subdivide them into 
follicles. The connective tissue of all these parts is composed of bundles of fibrous- 
connective tissue, more or less arranged as lamellae, separated by the ordinary flat- 
tened connective-tissue corpuscles, and great numbers of small lymph-corpuscles. In 
the capsule and the larger septa we meet with a small amount of elastic tissue in the 
form of networks of fine elastic fibres. 

The capsule is surrounded by a continuation of the pleura, a delicate connective- 
tissue membrane with networks of elastic fibrils and numerous capillary blood-vessels, 
a plexus of nerve fibres and a few lymphatic vessels ; towards the pleural cavity it is 
covered with a single layer of endothelium. 

B. The Gland Substance. 

The follicles are very irregular in shape, most of them being oblong or cylindrical. 
Near the capsule they are well defined from one another, and present a polygonal 
outline, often very regular ; towards the interior of the gland the follicles become more 
or less fused. 

Each follicle consists of a cortical or peripheral and a medullary or more or less 
central portion (Watney) ; the relation between the two, as regards amount, is not 
everywhere constant, but in most instances the cortical portion is greater in extent 
than the medullary. The medulla of neighbouring follicles is occasionally continuous 
(Watney). 

The matrix of the follicles is v. fine reticulum, differing from the adenoid reticulum, 
described in the preceding chapter, chiefly in the fact that in the thymus the 

D D 



1 66 ATLAS OF HISTOLOGY. 

reticulum still presents its embryonal aspect, being composed of nucleated branched 
cells. These cells consist of a flattened body with broad platelike sections (Afanassiew) ; 
numerous delicate filamentous and membranous processes are joined together so as to 
form the reticulum. 

The reticulum of the medulla contains coarse and short fibres ; those of the cortex 
are finer and longer (Watney). 

In the meshes of this reticulum lie the ordinary lymph-corpuscles, as described in 
connection with the adenoid tissue of the other lymphatic glands ; each lymph-corpuscle 
consists of a spherical nucleus, deeply staining in the different dyes, and of a very 
delicate zone of protoplasm. In the cortex of the follicles these lymph-corpuscles 
more or less completely fill the meshes of the reticulum ; in the medulla they are by 
far not so numerous. To the meshes of the reticulum appertain also endotheloid 
cells, transparent large cells, each with a transparent large oval nucleus. In the medulla 
these cells are very numerous, and regularly distributed, in such a manner that each 
of them fills the greater part of a mesh of the reticulum. Hence the lymph-corpuscles 
are here reduced to a narrow zone between the branches of the reticulum and the 
endotheloid cells. The effect of this arrangement is that the medulla is at once very 
conspicuous by its transparency and by the few lymph-corpuscles limited chiefly to 
the sides of the meshes of the reticulum. 

These endotheloid cells are also present in the cortex, but being smaller, a greater 
section of each mesh of the reticulum is filled with the lymph-corpuscles. In many 
places the endotheloid cells of the medulla, occasionally also of the cortex, are less 
transparent, being more granular, and include one, two, or three nuclei (large granular 
cells of Watney). From these to multinuclear giant cells all transitional forms may be 
met with. 

The so-called concentric corpuscles are protoplasmic masses of various sizes ; they 
occur in the medulla, and each consists of a central nucleated granular part, around 
which are placed, more or less concentrically, flattened nucleated endotheloid cells 
(Watney). 

According to Afanassiew the concentric corpuscles are developed in blood-vessels 
by a multiplication of the lining endothelium ; hereby the vessel becomes gradually 
obliterated, and the involution of the gland is thus initiated. According to Watney they 
are, on the contrary, concerned in the formation of blood-vessels and connective- 
tissue trabecular 

Each follicle possesses a network of capillaries, chiefly belonging to the cortex, 
and radiating from the periphery towards the centre ; the medulla possesses larger 
vessels than the cortex (Watney). In the dog the larger vascular branches penetrate 



BLOOD-VESSELS OF THYMUS GLAND. 167 

into the centre of the follicle before giving off the capillaries for the cortex (Kolliker, 
Afanassiew). 

As in the adenoid tissue of other lymphatic glands, so also here the blood-vessels 
obtain from the reticulum a special adventitious sheath. 

Lymph-sinuses may be seen occasionally surrounding a greater or smaller portion 
of the periphery of the follicles (Klein). 



d d 2 



1 68 ATLAS OF HISTOLOGY. 



CHAPTER XXII. 
LYMPHATIC VESSELS. 

i. The large lymphatic trunks, as ductus thoracicus and tributaries, have a structure 
in some respects similar to veins, but differing from these in the extreme thinness of 
their wall as compared with the large lumen. (a) A delicate adventitia of fibrous- 
connective tissue forms the outer boundary ; (6) next comes the media, a circular 
layer of unstriped muscle cells ; (c) on the inner surface of this is a fine elastic 
membrane, the intima, composed chiefly of a network of longitudinal elastic fibrils ; the 
inner boundary is formed by (d) a single layer of elongated nucleated endothelial plates 
with more or less sinuous outlines. 

The semilunar valves are folds of the intima and the endothelium. 
2. The microscopic lymphatic vessels, such as are present in great numbers in most 
tissues and organs, are tubular structures; many of them possess valves and corresponding 
saccular dilatations ; their wall is simple, being, like that of capillary blood-vessels, a 
single layer of endothelial plates. The endothelial cells are more or less elongated and 
possess each an oval excentric flat nucleus : their structural characters have been 
described and illustrated in Chapter III., and they have been illustrated on Plate VI. 
The lumen of the lymphatics bears no relation to their wall, for lymphatics that are 
not broader than blood capillaries, as well as such that are many times larger, have an 
equally delicate endothelial membrane for their wall. Hence it follows that, unlike blood- 
vessels, they cannot rely on the firmness of their own wall for keeping their lumen free, 
but must be supported in this by the surrounding connective tissue. And indeed, these 
vessels will be found invariably collapsed and lost to view, as soon as the tissue in 
which they are embedded is allowed to shrink or does otherwise contract 

The lymphatics in all tissues and organs are connected into a plexus, the density 
and arrangement of which varies in different localities ; all the vessels of such a plexus 
that possess valves and corresponding saccular dilatations are considered as trunks, 
whereas those parts of the plexus that have no valves are lymphatic capillaries. The 
trunks are, as a rule, more tubular in character than the capillaries, which are often 
irregular, saccular, or cleft like cavities ; besides, the endothelial cells forming the wall 
of a trunk are generally elongated, whereas those of a capillary are shorter and their 



PERI VA SCULAR L YMPHA TICS. 1 69 

■ . a 

outlines more sinuous (see Plate VI. fig. XIII.). It is to be borne in mind, however, 
that this latter condition may be met with also in the trunks, whose wall has become 
much shrunk. The size of the vessel is no distinguishing character, for in many 
organs we find capillaries of greater calibre than the trunks. 

In some localities we find one or the other blood-vessel completely enshcathed in 
a lymphatic capillary, perivascular lymphatic (Robin, His, Strieker, MacGellavry and 
others). 

3. In all instances the lymphatic capillaries bear a definite relation to the tissue to 
which they belong, having their rootlets in this latter. It is this: the capillaries open 
into a system of lacunae connected with each other by finer or broader canals or clefts : 
this system, which is the lymph-canalicular system of v. Recklinghausen, is moulded, as 
it were, in an albuminous, semifluid interstitial substance, and represents, as has been 
mentioned on former occasions (Chapter IV.), the spaces containing the connective-tissue 
corpuscles, these forming, as it were, an endotheloid lining for it. While, therefore, the 
cavity of the capillary lymphatic is in a free communication with the lymph-canalicular 
system, its endothelial wall is continuous with the connective-tissue corpuscles contained 
in the former (Kolliker, v. Recklinghausen, Klein). Such we find the relation of the 
lymphatic capillaries to the surrounding tissue in the lung, serous and synovial mem- 
branes and membranes of the brain and cord. In some places, such as cornea, cartilage, 
white and grey matter of the brain and cord, the lymph-canalicular system is the chief 
and to a great extent the sole representative of the lymphatics. 

The nature of the lymph-canalicular system differs, however, considerably in dif- 
ferent organs, being dependent on the nature and arrangement of the matrix. The 
most typical and regular form of it we meet with in the cornea, lung, serous membranes 
and bone, being uniformly branched and anastomosing lacunae, lined by the corresponding 
corneal corpuscles, branched connective-tissue cells, or bone corpuscles respectively. 
In tendon, fascia and aponeurosis, owing to the peculiar arrangement of the connective- 
tissue bundles (see Chapter IV.), it consists of straight and continuous clefts and 
channels situated between groups of connective-tissue bundles ; in striped and unstrip-d 
muscle, and nerves, there are likewise long and straight clefts and spaces extending 

between the individual fibres. 

In the skin and mucous membranes and similar masses of ordinary fibrous-con- 
nective tissue the lymph-rootlets are of a very irregular nature, viz. spaces left between 
groups or trabecule of bundles crossing each other in a complex manner, interfascicular 
spaces. As has been mentioned on a former occasion, the connective-tissue corpuscles are 
applied to the surface of the trabecule so as to be at the same time the lining cells of 
those spaces. In the loose subcutaneous and submucous tissue there are all gradations 



I/O 



ATLAS OF HISTOLOGY. 



between interfascicular spaces or sinuses lined by a complete endothelium, and conse- 
quently representing a lymphatic capillary, and small irregular lacunae lined only on 
one side by a branched connective-tissue cell. 

4. As has been mentioned in a former chapter, the wall of capillary blood-vessels does 
not present any obstacle to the passage of formed particles (blood-corpuscles or pigment). 
This takes place through the interstitial substance (stigmata) acting as cement between 
the endothelial plates constituting the wall of the capillary. It has also been mentioned 
that the connective-tissue corpuscles of the surrounding tissue are connected with the 
wall of the capillaries : this connection consists in a continuity of the interstitial albuminous 
cement-substance of the endothelial wall with the same albuminous substance in which is em- 
bedded, as above stated, the lymph canalicular system or the connective-tissue corpuscles 
respectively. Thus fluid or formed matter escaping from the blood-vessel (through the 
interstitial substance) passes into the lymph-canalicular system (Arnold, Foa), lined by 
the connective-tissue corpuscles, and from here freely into the capillary lymphatics. And 
this passage of plasma from the capillary blood-vessels through the lymph-rootlets into the 
lymphatic capillaries represents the normal stream that uniformly percolates the tissues. 
This stream is caused, in the first place, by the difference of pressure that exists in the 
capillary blood-vessels and in the lymphatics, in the former being positive, in the latter 
negative ; and in the second place, by the peculiar distribution of the blood and lymph- 
capillaries, the former holding, as it were, the centre of a definite area, while the latter 
belong to its periphery (v. Recklinghausen), and hence the tendency of the plasma to 
uniformly percolate the tissue intervening between the two systems of vessels. The 
passage of formed matter, such as colourless and coloured blood-corpuscles or pigment 
matter, from the blood-vessels, into the lymph-canalicular system, and hence into the 
lymphatics, is well illustrated in inflammation (Cohnheim, Hering, Arnold, Klein, and 
others), and in the experiments of Klein, Arnold, Kuttner, and others, where pigment 
matter (Berlin blue or indigo sulphate of sodium) introduced into the organism of the 
living guinea-pig, rabbit, or frog can be easily traced through the lymph-canalicular 
system into the lymphatics. 

5. The lymphatics of the serous membranes. 

The endothelium covering the free surface of the serous membranes has been 
minutely described in all its details in Chapter III. ; and likewise the connective-tissue 
matrix and its cells in Chapter IV. Bizzozero showed in the serous membranes of man a 
thick membrana propria, ' limiting membrane,' separating the endothelium from the ground 
substance. Networks of blood capillaries occur in all parts of the serous membranes, 
especially in those parts that contain patches, nodules, or cords of adenoid tissue or fat 
tissue. The sympathetic nerves mentioned in a former chapter split up into minute 



LYMPHATICS OF SEROUS MEMBRANES. 1?l 

branches which are connected into a plexus ; from this come off fine non-medullated 
fibres which are characterised by their relatively long course; according to Cyon they 
terminate in free endings in the tissue, but according to Klein and Gempt they are con- 
nected into a network ; most of the nerves belong however to the blood-vessels. 
The nerve branches contain occasionally small groups of ganglion cells. 

The lymphatics are numerous in all serous membranes ; the tubular trunks possess 
valves, and some of the larger vessels also a layer of circular muscle cells : they form 
plexuses chiefly in the neighbourhood and around the larger bood-vessels ; some of these 
latter are occasionally ensheathed in a continuous perivascular lymphatic tube (omentum 
of rabbit, mesentery of frog) or in an intercommunicating system of lymph-sinuses lined 
with endothelium (mesentery of toad). The parts of the serous membrane situated 
between the large vascular trunks contain the lymphatic capillaries which are every- 
where connected with the lymph-canalicular system, as described above. 

The lymphatics of the central tendon of the diaphragm and the intercostal pleura 
possess special characters. 

a) The central tendon of the diaphragm of rodents. The matrix of this is a double 
layer of tendon bundles ; one layer, nearest to the peritoneum, is composed of bundles 
more or less radiating from the centre towards the periphery, while the other, nearest to 
the pleura, contains more or less circular bundles, crossing the former under a right 
angle. Between groups of these bundles are lymphatic channels (Ludwig and 
Schweigger-Seidel); they are lymphatic capillaries, the wall of which is a single layer 
of endothelial plates with sinuous outlines : they are the straight lymphatic capillaries 
(Klein). Those of them that belong to the radiating layer of tendon bundles possess 
naturally a radiating direction, and represent the superficial, while those of the circular 
layer are arranged circularly, crossing the former under a right angle and represent the 
deep straight lymph-capillaries. But the vessels of both layers form an intercommu- 
nicating and therefore single system, being connected with each other by small openings, 
chiefly at the point of crossing. 

This matrix of tendon bundles is covered on the pleural surface with a delicate 
but dense connective-tissue membrane, the pleura, which on its free surface is covered 
with a layer of ordinary flattened endothelial plates. There is always a more or less 
continuous subendothelial membrana propria, a single layer of flattened cell. These 
are either unbranchecl, and touch each other in straight lines like an endothelium, or 
they are branched and form a network. The peritoneal surface of the tendon bundles is 
also covered with a delicate connective-tissue membrane, the peritoneum ; but this 
membrane is complete only where it stretches over the tendon bundles themselves, while 
that portion of it that covers the radiating or superficial straight lymph-capillaries is a 



ATLAS OF HISTOLOGY. 
fenestrated membrane (Ludwig and Schweigger-Seidel), viz. a plexus of anastomosing 
trabecule with smaller or larger oval or spherical meshes. The endothelium covering 
this fenestrated part, that is above the straight lymph-channels, is composed of small 
more or less germinating endothelial cells, while that above the tendon bundles consists 
of the ordinary large endothelial plates, as mentioned in Chapter III. 

Between the pleural serosa and the circular layer of tendon bundles lies a dense 
plexus of lymphatic vessels with valves, their wall is a single layer of elongated 
endothelial cells (see fig. Xll.We VI.). In connection with this plexus, which repre- 
sents the 'plexus of pleural lymphatics of the central tendon,' are (a) capillaries that have 
their roots in the Iymph-canalicular system of the pleural serosa itself, and (6) the circular 
or deep straight lymphatics, which, as we mentioned above, form, with the radiating 
or superficial straight lymphatics, an intercommunicating system. 

The plexus of pleural lymphatics is arranged as an anterior and posterior 
system (Klein) ; the former is symmetrically distributed over the two anterior quadrants, 
and the same is the case with the latter, viz. one for each of the two posterior quad- 
rants. The pleural lymphatics of both sides of the anterior system, as well as those 
of both sides of the posterior system, communicate with each other by intermediary 

branches. 

The efferent trunks of the anterior system run near the margin of the central 
tendon towards the xyphoid cartilage, where the branches of the two sides anastomose 
with one another and, freely intercommunicating, ascend on the posterior surface 
of the sternum towards the jugular incision of the manubrium sterni, and finally enter 
a lymphatic gland, one for each side. The efferent trunks of the posterior system 
are fewer and larger, and finally collect into one or two short large vessels for each 
side, which freely empty themselves into the thoracic duct. 

Bizzozero and Salvioli have shown that the arrangement of the lymphatics in the 
muscular portion (pars costalis) of the diaphragm is similar to that of the central tendon. 

In connection with the radiating straight lymphatic capillaries in rodents there 
are smaller and larger sinuous or saccular lymphatic capillaries (Klein), they are chiefly 
near the middle line of both the anterior and posterior quadrants. Bizzozero and Salvioli 
showed them to exist also in the human diaphragm, especially in the ' zona peritendinea.' 

According to Rajewsky the arrangement of the lymphatic system of the central 
tendon in man is the same as in rodents. 

The membrana propria or limiting membrane described by Bizzozero and Salvioli 
of the peritoneal surface of the human diaphragm is perforated, above the radi- 
ating straight lymphatics, and also above the aforesaid lymph-sinuses, by minute 
holes. 



STOMA TA OF THE DIAPHRAGM. t;3 

The superficial or radiating straight lymphatic capillaries are in open communication 
with the peritoneal cavity through stomata (Oedmanson, v. Recklinghausen) ; the meshes 
of the fenestrated portion (Ludwigand Schweigger-Seidel) of the peritoneum mentioned 
above as bridging over those capillaries, and in man the holes of the subendothelial 
limiting membrane (Bizzozero and Salvioli), together with discontinuities in the endothe- 
lium of the surface and of the straight lymphatic capillaries, contribute to form those 
stomata. I have shown that the endothelial cells surrounding r rather lining them 
(stomata vera) are germinating cells. 

The deep or circular straight lymphatic capillaries, which, as has been mentioned 
above, are in open communication with the superficial or radiating ones, empty them- 
selves into the pleural lymphatics (Ludwig and Schweigger-Seidel), both the anterior 
and posterior system, so that they are able to discharge their contents in two directions 
at the same time (Klein), viz. towards the lymphatics constituting the anterior as well 
as towards those constituting the posterior system. 

The current passing through the lymphatics of the diaphragm is then : from the 
free peritoneal surface of the diaphragm, that is the peritoneal cavity, through the sto- 
mata vera into the superficial or radiating straight lymphatic capillaries, hence into the 
deep or circular straight ones : hence the current may pass in two directions, viz. (a) 
into the plexus of lymphatic vessels forming the anterior system, and (6) into that of the 
posterior system ; through the efferent trunks of the former the current passes a long 
and circuitous way (along the sternum) into a lymphatic gland, whereas through the 
efferent trunks of the latter it reaches in a short and unimpeded manner directly the 
thoracic duct. Hence the pleural lymphatics of the posterior system are easier filled 
and easier emptied than those of the anterior system (Ludwig and Schweigger-Seidel, 
Klein). 

The respiratory action of the diaphragm is the principal moving cause of the circu- 
lation in the lymphatics of the latter (Ludwig and Schweigger-Seidel) thus : during 
inspiration the straight lymphatics (both the superficial and deep ones) become distended 
owing to the descent of the central tendon and consequently the greater separation of 
its bundles from one another, while at the same time the pleural lymphatics become 
compressed ; in this distended state of the superficial straight lymphatic capillaries the 
above stomata necessarily are wide open, and there exists therefore a tendency on the 
part of the straight lymphatic capillaries to absorb plasma, cells, or other formed matter 
that happens to be present on the peritoneal surface of the diaphragm. But at the same 
time, owing to the compression of the pleural lymphatics, these will discharge their 
contents into the efferent trunks. During expiration the straight lymphatics become com- 
pressed owing to the tendon bundles becoming again closer, the pleural lymphatics being 

E E 



ATLAS OF HISTOLOGY. 
1 74 

at the same time distended, for during the ascent of the central tendon the area of 
its pleural surface becomes enlarged. Hence the effect of the movement of the 
diaphragm on its lymphatics in inspiration is the reverse from that in expiration, since 
during the latter the straight lymphatic capillaries become compressed and therefore dis- 
charge their contents ; these are readily received by the pleural lymphatics, distended 

during this period. 

The action of the respiratory movements of the diaphragm is, therefore, that of a 
pump (Ludwig and Schweigger-Seidel), but of one with two cylinders (Klein), owing to 
the straight lymphatics emptying themselves in two directions, viz. into the anterior and 
posterior systems, as mentioned above. 

The direct absorption of formed matter, milk, blood, &c., placed on the peritoneal surface of 
the central tendon of rabbit by the lymphatics of this organ has been first shown by v. Reckling- 
hausen, and Rajcwski proved the same also for the human diaphragm. Ludwig and Schweigger- 
Seidel then proved this to be dependent chiefly on the respiratory movements ; Klein demonstrated 
the lymphatics in their different relations to one another by injecting Berlin blue into the peritoneal 
cavity of the living rabbit and examining the diaphragm after several hours. 

b) In the intercostal pleura the lymphatics are arranged as a plexus of superficial 
and one of deep lymphatics (Dybkovski) ; the vessels of the former correspond to straight 
lymphatic capillaries which open freely by stomata vera on the free surface, that is into 
the pleural cavity ; on the other hand they empty themselves into the plexus of deep 
lymphatics, which possess valves and the efferent trunks of which pass through the 
subserous tissue outwards. 

As in the zona peritendinea of the diaphragm, so also m the pleura costalis and 
intercostalis of man, Bizzozero and Salvioli showed the existence of small holes in the 
subendothelial membrana propria or limitans ; these holes, together with the holes 
between the endothelial cells of the surface, form the stomata. The relation of the pul- 
monary pleura with the pleural cavity will be considered in the chapter on the Lung. 

Dybkovski proved the passage of pigment matter from the pleural cavity through 
the stomata into the lymphatic system of the intercostal pleura, and likewise that, as 
in the case of the diaphragm, the respiratory movement has a direct influence on the 
absorption, viz. acting as a pump. 

6. The synovial membrane possesses, according to Tillmanns, a rich network of 
lymphatics, of which there is a plexus immediately underneath the endothelium of the 
surface ; the deeper vessels mostly accompany the large blood-vessels. In the tendinous 
parts Tillmanns finds a network of lymphatic clefts situated chiefly between the bundles 
of connective tissue, similar as in tendinous tissue of other localities. 

In certain places of the knee-joint of rabbit Nicoladoni described numerous nerve branches, 
from which fine nerve fibres come off; some of them terminate in a network, others belong to 



STOMA TA OF SEROUS MEMBRANES. l?5 

blood-vessels, and a third group enter Pacinian corpuscles. Krause observed in the synovia] 
membranes of the joints of the human fingers mcdullatcd nerve fibres terminating in peculiar tactile 
corpuscles, ' articulation-nerve corpuscles.' 

7. Besides the true stomata mentioned above as occurring on the peritoneum of the 
diaphragm and on the intercostal pleura, there are also true stomata in other membranes, 
as in the mesentery, omentum, pleura mediastini ; they are mostly marked by two or 
three or more germinating cells surrounding them. These cells, when ripe, become 
detached and may be at once absorbed as lymph-corpuscles (Klein). The best stomata are 
seen on the mesogastrium and mesentery of frog and the septum cisterns lymphatics 
magnre of the same animal. In the latter membrane the stomata are short canals by which 
a direct communication is established between the peritoneal cavity and the large cistern 
behind; in the former membranes the stomata open into a superficial lymphatic. In 
female individuals, especially during the spawning season, both on the mesogastrium and 
mesentery (Klein), as well as on the peritoneal surface of the septum cist, lymph, magn. 
(Dogieland Schweigger-Seidel, Klein), the endothelial cells lining the stomata are ciliated 
and often germinate (Klein). (See also Chapter III., Plate V.) 

8. The epithelium lining mucous membranes and secreting glands and the endo- 
thelium covering serous and synovial membranes or lining blood-vessels and lymphatics 
bear a definite relation to the lymph-canalicular system of the tissue underneath or outside 
respectively. This relation may be shortly described by saying that the hyalin albu- 
minous interstitial or cement-substance, i.e. the substance separating the individual epi- 
thelial or endothelial cells, is directly continuous with the albuminous interstitial substance 
in which the lymph-canalicular system is embedded (see above), so that fluid and formed 
matter can pass freely from the intra-epithelial cement-substance into the lymph-canalicular 
system underneath, or vice versa. And also the connective-tissue corpuscles contained 
in the lymph-canalicular system are continuous with branched nucleated cells which 
extend into the epithelium, and whose processes are lost in the cement-substance of the 
epithelium. These intra-epithelial connective-tissue corpuscles (pigmented or unpig- 
mented) have been mentioned before on more than one occasion. The absorption through 
the epithelium and endothelium is therefore carried out by means of the interstitial 
cement-substance, hence the current passes into the subjacent lymph-canalicular system, 
and finally into the lymphatic vessels. The absorption of fluid and formed matter is 
carried out in the same manner in every epithelium (including that of the villi of small 
intestine, bronchi, and alveoli of lung, glands, &c.) and endothelium, viz. through the 
interstitial substance and not through the substance of the epithelial or endothelial cells 
themselves ; this mode of absorption may be described as taking place through pseudo- 
stomata, as different from that through true stomata (stomata vera). 

E E 2 



1?6 ATLAS OF HISTOLOGY. 

By the experiments of Thoma, Arnold, and others it has been proved that indigo 
sulphate of sodium injected into the circulating system of frog is eliminated from the 
blood-vessels through the paths just mentioned, only, of course, in a reversed order, viz. 
from the capillary blood-vessels (through the stigmata) into the lymph-canalicular system, 
hence into the cement-substance of epithelium or endothelium. 

9. The lymph-channels of connective tissue have been described above, and it 
remains here to mention a few special points : 

a) The lymph-clefts between groups of bundles in tendons, fasciae and ligaments, 
mentioned above, are not the ultimate rootlets of the lymphatic system in these organs, 
for injection-matter may pass from the lymph-clefts into the albuminous cement-sub- 
stance between the individual bundles forming these groups (Key and Retzius, 

Herzog). 

b) Genersich, Ludwig, and Schweigger-Seidel demonstrated on the inner surface of 
fasciae and aponeuroses a plexus of lymphatic capillaries, the greater number of which 
run parallel with the connective-tissue bundles; they are connected by a few short cross- 
branches. On the outer surface, however, the lymphatic capillaries form a plexus with 
polygonal meshes. From these proceed the efferent trunks possessed of valves. 
Genersich also showed that the first-named capillaries, viz. the straight vessels on the 
inner surface, bear the same relation to the lymphatics on the outer surface, as the straight 
lymphatic capillaries of the central tendon to the plexus of pleural lymphatics of this 



same organ. 



Injection matter, introduced into the lymph-clefts situated between striped muscle 
fibres, passes into the straight lymphatics of the inner surface of the corresponding fascia 
or aponeurosis, and from here through oblique vessels into the plexus of lymphatics of 
the outer surface (Genersich, Ludwig, and Schweigger-Seidel). 

The lymph-clefts between the individual muscle fibres are just like those between the nerve 
fibres, spaces, whose boundary is formed on one side by the muscle fibre or nerve fibre respectively, 
and on the other by the connective tissue described and figured in former chapters as endomysium 
or endoneurium respectively ; they pass into lymphatic capillaries situated in the perimysium. 

In the ligamentum nucha? of ruminants Schwalbe proved the existence of lymphatic 
vessels, running longitudinally and connected into a network by fine transverse 
branches. They are situated in the connective tissue separating the bundles of elastic 
fibres (see the chapter on elastic tissue). In connection with them are lymph-channels 
and clefts of the connective-tissue between the elastic fibres. 

10. The lymphatics of cartilage. 

The perichondrium of all cartilages possesses a plexus of lymphatic vessels. The 
lacunae in which the cartilage cells of hyaline and elastic cartilage lie are connected with 



LYMPHATICS OF CARTILAGE AND BONE. 177 

one another by fine canals, and also with the lacuna of the cells of the perichondrium ; 
so that also in these cartilages we meet with a lymph-canalicular system similar to that 
of the cornea. This lymph-canalicular system is in direct communication with the 
lymphatic vessels of the perichondrium. Budge injected it in the articular cartilage 
(of calf) from the lymphatic vessels of the periosteum, and Nykamp saw it indicated in 
hyaline cartilage of rabbit by granules of indigo carmine, this substance having been 
injected into the peritoneal cavity several hours previously. Arnold saw the indigo 
sulphate of sodium, which had been previously injected into the circulating blood, 
deposited in fine lines passing in a radiating manner through the capsules of the 
cartilage cells. 

Consequently the canaliculi by which neighbouring lacuna anastomose and which 
permeate the hyaline matrix, increase greatly in numbers as they pass through the 
capsule immediately surrounding the lacuna of the cartilage cell. 
1 1. The lymphatics of bone. 

The periosteum possesses a network of lymphatic vessels which are in connection 
with the lymph-clefts (lymph-canalicular system) of the fibrous-connective tissue of that 
organ. According to Budge the lymphatics of the periosteum of the metatarsus of 
calf are arranged in several layers, and in most instances accompany the blood-vessels. 
Schwalbe found in the human femur and tibia lymphatic vessels only in the superficial 
layers of the periosteum, but saw numerous clefts, especially between the inner and 
outer layer, anastomosing with those vessels. 

The periosteal lymphatics are in communication with the lymphatics of the Haver- 
sian canals (Budge, Schwalbe) ; these are either perivascular lymphatics totally invagi- 
nating the blood-vessel of the Haversian canal (Rauber, Budge, Schwalbe) or, as in the 
large Haversian canals, they are separate lymphatics accompanying the blood-vessels. In 
both cases the wall of the lymphatics is represented by a single layer of endothelium. The 
lymphatics of the Haversian canals are in open connection with the lacunar and canaliculi 
of the bone corpuscles (Budge), and these represent therefore a similar lymph-canalicular 
system as that of the cornea (see also chapter on Bone). The marrow also contains lym- 
phatic vessels, which generally accompany or invaginate the veins and capillaries (Budge). 
Schwalbe demonstrated a continuous endothelium on the surface of the yellow 
marrow and on that of the cord of vessels lying in the canalis nutritius. 

Arnold recognised the course of the lymphatic system, as just described, by a deposit 
of indigo sulphate of sodium taking place in the lymphatic system of bone of frog, that 
substance having been previously (24 to 48 hours) injected into the circulating system. 

12. The lymphatics of the nervous system have been described and figured in pre- 
vious chapters in connection with these tissues. 



, 7 8 ATLAS OF HISTOLOGY. 

13. The lymphatics of the alimentary, respiratory, urinary and genital organs, those 
of the skin and sense organs, will be described in connection with these various tissues. 

14. Development of lymphatic vessels. The lymphatic vessels develop, both under 
normal and pathological conditions, after the same plan as blood-vessels, viz. by a process 
of vacuolation of branched cells (Klein) ; from the wall of a lymphatic vessel solid proto- 
plasmic filamentous processes grow out, and these, gradually becoming hollowed out, 
form lateral branches. In some cases we find a series of vacuolated cells, vesicles, 
which having been brought into contact are gradually fused so as to form one continuous 
vessel. In other instances a single cell grows into a nucleated cylindrical, single or 
branched band or filament, which by vacuolation becomes converted into a vessel, in the 
same manner as described of blood-vessels in Chapter XIX. The differentiation of the 
protoplasmic wall of the young lymphatic into endothelial cells occurs at a later stage. 



PLATE XXX. 

Fig. XIII. Copied from Klein's 'Anatomy of the Lymphatic System,' I. 
From the central tendon of rabbit after staining with nitrate of silver, showing the 
connection of a lymphatic capillary, indicated on the left and upper part of the figure by 
its endothelial wall, with the lymph-canalicular system of the pleural serosa ; the lacunae 
are represented as more or less branched clear spaces in the dark ground-substance. 
In some lacunae a nucleus is seen belonging to the connective-tissue corpuscle. 

/. Transition of the endothelial cells of the lymphatic capillary into the connective- 
tissue corpuscles contained in the lymph-canalicular system. Magnifying power 
about 300. 

Fig. XIV. From a preparation of the gall-bladder of guinea-pig. 

/. Lymphatic vessels underneath the serous covering of the gall-bladder, forming a 
plexus. The wall of the lymphatics is marked blue, owing to a precipitate on the inner 
side of their wall of Berlin blue injected by the method of ' puncture.' 

v. Semilunar valves seen in profile and indicated by an accumulation of injection 
matter. 

b. Ramifications of blood-vessels, arteries, capillaries, and veins, belonging to the 
mucous membrane of the gall-bladder, and accidentally injected at the same time. 

Magnifying power about 25. 

Fig. XV. Copied from Klein's ' Anatomy of the Lymphatic System,' I. 

Part of the peritoneal surface of a silver-stained preparation of the central tendon 
of diaphragm of rabbit. 












^ 




■ 












/ 







&- 



■ 






■ 



















. - 






i 



DEVELOPMENT OF LYMPHATICS. 179 

/. Superficial straight lymphatic capillary, contained between the radiating tendon 
bundles. 

s. Stomata surrounded by germinating endothelium and leading from the free 
surface into the straight lymphatic ; some of the stomata are open, others collapsed. 

t. Part that corresponds to tendon bundles ; the endothelial cells covering this part 
are larger than those over the lymphatic capillary (see Chapter III.). 

Figs. XVI. and XVIII. represent developing lymphatic vessels of the tadpole's 
tail ; magnif. power about 350. These vessels develop from branched corpuscles in the 
same manner as the blood-capillaries described and figured in a previous chapter, viz. 
by a process of vacuolation. The minute spikes and filaments of the wall of the young 
lymphatics are very numerous and quite characteristic. In some parts of the tadpoles 
tail it is not easy to distinguish a developing blood-vessel from a young lymphatic, but 
as a rule this distinction is facilitated by noticing that the wall of the former is coarser 
than that of the latter, that it possesses few of the above processes, and that it can be 
traced to a vessel that contains blood-corpuscles. 

a. Parts that are still composed of solid protoplasm. 

Fig. XVII. From a horizontal section through the superficial part of a thymus of 
calf, viewed under a lens ; showing in the centre a follicle of polygonal shape and similarly 
shaped follicles around it. This polygonal shape does not, however, indicate that the 
follicles are polyhedral, but only that the part of the follicle next to the capsule is so 
shaped. The clear lines between the follicles indicate the interstitial connective tissue 
separating them. The distinction into a transparent medullary and deeper stained 
cortical portion is well shown. 

Fig. XIX. Copied from Klein's 'Anatomy of the Lymphatic System,' II. 

a. The ciliated columnar epithelium lining a bronchus. 

b. The branched connective-tissue corpuscles of the mucosa ; they arc connected 
with similar branched corpuscles in the epithelium, whose processes reach up to the fn 1 
surface and are embedded and lost in the interstitial cement-substance — the pscudo- 
stomata. 

The connective-tissue corpuscles are contained in the lymph-canalicular system 
(see a previous page), and it may be therefore said that the interstitial substance of the 
epithelium acts as rootlets of the lymph-canalicular system of the mucosa. 

Fig. XX. Copied from Arnold, ' Virchow's Archiv/vol. Ixxiii. Showing the excretion 
of indigo sulphate of sodium in fine lines passing radially through the capsule of the 
cartilage cells. When seen from above these lines appear of course as fine dots. 

Fig. XXI. Copied from Klein's 'Anatomy of the Lymphatic System,' I. Showing 
the lymphatics of part of the central tendon of rabbit injected with Berlin blue, that had 



i So ATLAS OF HISTOLOGY. 

been introduced into the peritoneal cavity of the living animal several hours previously. 
Magn. power about 90. 

a. Pleural lymphatics, i.e. vessels that belong to the pleural section of the dia- 
phragm ; the vessels are possessed of valves and corresponding saccular dilatations. 

I). Superficial straight lymphatic capillaries situated between the radiating tendon 
bundles ; they are connected with the deep straight lymphatics which cross them, 
and, as has been mentioned on a former page, are situated between the circular tendon 
bundles ; the deep straight lymphatics lead into the above pleural vessels. 

Fig. XXII. Copied from Nykamp, ' Archivf. mikrosk. Anat.' XIV. Showing the 
excretion of granules of indigo carmine into the lacunae and canaliculi of the cartilage 
cells, c, as well as into those of the periosteum,/. 



iSz 



CHAPTER XXIII. 

TEETH. 

The hard parts of a human tooth are: (a) the enamel, substantia adamantina ; (i) the 
dentin or ivory; (c) the cement, or substantia osteoidea. The soft parts are: (i) the 
dental pulp ; (2) the periosteum ; and (3) the gums. 

a) The enamel covers the crown of the tooth. It consists of closely placed solid thin 
prisms, enamel prisms, extending, in a direction vertical to the surface, from this latter 
to the subjacent dentin : they appear hexagonal when viewed in transverse section. The 
prisms are arranged in bundles. These cross each other, so that on a longitudinal section 
of tooth alternate layers of longitudinally and transversely cut prisms are visible. Hereby 
the appearance of alternate light and dark stripes is produced. Besides this inequality 
in appearance, there are the 'brown parallel stripes of Retzius,' consisting of horizontal 
curved lines running more or less parallel with one another, often very closely placed. 
Their significance is not definitely ascertained, inasmuch as deposit of pigment (Hertz) 
or successive formation of enamel (Kolliker) is given as its cause. Each enamel prism 
when isolated by dilute HC1 shows regular transverse markings and varicosities, owing 
probably to a successive formation oi its parts (Hannover, Hertz). By continued 
maceration in HC1 they disintegrate into short cubical pieces (Waldeyer). 

The enamel consists chiefly of lime salts, phosphate and carbonate of lime, a trace of fluoride of 
calcium, and very little phosphate of magnesia ; a small percentage (1— 35) of organic matter is 
also contained in it. 

The enamel prisms, although closely placed side by side, are nevertheless separated 
from one another by a very thin layer of hyaline interstitial substance. In the parts of 
the enamel bordering on the dentin are often found shorter or longer canals and lacunae 
between layers of prisms, and leading into the interglobular spaces of Czermak, situated on 
the surface of the dentin. A delicate cuticle (Kolliker, persistent capsule of Nasmyth) 
covers the outer surface of the enamel of young teeth : it is composed of a layer of non- 
nucleated horny scales. 

b) The dentin or ivory (osteodentin, Tomes) consists of the following parts : (a) a 
homogeneous hard ground substance ; this contains, embedded in a dense reticular matrix 
of organic substance, lime salts similar to the ground substance of bone ; (£) long fine 
canals, dentinal canals, passing through the whole thickness of the dentin in a spiral 

F F 



,g 2 ATLAS OF HISTOLOGY. 

manner and in a direction vertical to the surface of this substance. These canals com- 
mence at the pulp cavity, and become gradually finer as they approach the enamel. 
Numerous fine lateral branches unite them amongst each other. The wall of each canal 
is formed by an elastic membrane, dentinal sheath of Neumann ; this withstands acids 
and alcalies. (y) The cavity of each dentinal canal contains the deiifaial fibre of 
Tomes : this is a solid branched fibre, very elastic, and of a homogeneous structure. 
These fibres are regarded as the processes of nucleated cells lining the inner surface of 
the dentin or covering the outer surface of the pulp-tissue, generally called the layer of 
odontoblasts (Waldeyer). 

The dentinal canals pass, on the outer surface of the dentin, into the interglobular 
spaces of Czermak, or the granular layer of Purkinje. They are larger or smaller branched 
spaces intercommunicating with one another, and into them terminate the dentinal canals. 
Where the dentin is covered with enamel, viz. at the crown, the interglobular spaces 
extend as blind canals a certain short distance between bundles of enamel prisms, as 
mentioned above ; on the neck and fang, viz. where the dentin is in contact with the 
cement, the interglobular spaces are in direct communication with the bone lacunae and 
their canaliculi. Just as these latter contain nucleated branched cells, so do also the 
interglobular spaces include nucleated branched protoplasmic corpuscles : these are espe- 
cially distinct in young teeth (Waldeyer). The dentinal fibres are directly continuous 
with these cells, so that an anatomical connection is established between the odontoblasts 
and the cells of the interglobular spaces. According to Kolliker, Tomes, Wenzel, and 
others, the dentinal fibres penetrate also into the enamel. The interglobular substance 
of Czermak is imperfectly calcified dentin ; it is present in distinct and separate layers, 
more or less parallel to the surface of the tooth : these layers are the incremental lines 
of Salter. Owing to the curved indentations of the interglobular substance, the adjoining 
dentin matrix assumes the form of globular masses, dentin spheroids. ' The lines of 
Schreger ' are parallel to the surface, and are the optical effect of simultaneous curvatures 
of the dentinal fibres. 

c) The cement is osseous substance of the nature of ordinary osseous tissue, viz. a 
more or less lamellated bone matrix containing the bone corpuscles : lacuna? and 
canaliculi, and in these the nucleated bone cells (see Chapter IX.). The bone corpuscles 
are here exceptionally large, and their canaliculi very numerous. The cement is covered 
by the alveolar periost, to which it stands in the same relation as other bone substance to 
the osteogenetic layer of the periosteum (see Chapter IX.). The cement is generally 
thickest near the apex of the root. In very thick parts of cement Haversian canals with 
blood-vessels may be occasionally met with (Salter). Sharpey's fibres exist also in the 
cement ; they are well shown in cement of tooth of dog (Waldeyer). 



STRUCTURE OF THE PULP OF TOOTH. 183 

The tissue of the periosteum surrounding the cement differs in no respect from the 
osteogenetic layer of the periosteum, such as that covering the outer surface of the alveolus 
of the jaw. The mucous membrane of the gums will be described in connection with the 
mucous membrane of the oral cavity ; but its tendinous nature, its firm connection with 
the fibrous layer of the periosteum, the regular and beautiful papillae, and the fine prickle 
cells of the middle layers of the stratified epithelium, may be here mentioned. 

The pulp is a continuation of the alveolar periosteum. It consists of a great 
number of cells, these are chiefly branched cells, each with an oval or spherical nucleus ; 
the cell substance surrounding the nucleus is very small in amount, and is drawn out in 
two or three homogeneous long processes which at their extremities are richly branched ; 
by their anastomosis with one another they form a dense reticulum of homogeneous fine 
fibres, the matrix of the pulp tissue. A few spherical lymphoid corpuscles are to be mel 
with in it. 

At the periphery the cells of the dental pulp form two distinct strata of different 
cells. The outer stratum, that next to the inner surface of the dentin, is a layer of 
beautiful columnar cells ; their substance is a dense reticulum ; each cell contains an oval 
nucleus in the inner section. This layer is the layer of odontoblasts (Waldeyer, Boll). 
The cells are possessed of fine processes directed towards the pulp and connected with 
the cells of this latter. According to Waldeyer, Boll and others, the odontoblasts 
send processes into the dentinal canals as the dentinal fibres, and are also possessed of 
lateral processes by which they (odontoblasts) are connected with one another. 

The deeper stratum is composed of spindle-shaped or pyramidal cells wedging 
themselves in between the odontoblasts ; they are identical with the branched cells of 
the pulp, mentioned above, of which they are merely a dense superficial row. They are 
accordingly in connection with the reticulum of the pulp matrix, and also amongst each 
other. Each of them sends two or more filamentous processes towards the dentin, 
whose canals they enter as the dentinal fibres. 

[However great the authorities who maintain that the cells of the outer stratum, 
above referred to as the odontoblasts proper, send processes into the dentinal canals as 
the dentinal fibres, I must question the accuracy of this assertion, for I cannot find 
convincing evidence of those odontoblasts doing more than producing the dentin 
matrix, as will be described below. The dentinal fibres appear to me derived solely 
from the deep layer of cells which, as has been mentioned just now, are wedged in 
between the former. — E. K.] 

Boll first pointed out the great number of non-medullated nerves in the superficial 
part of the pulp-tissue. The fibrils ascend from here between the odontoblast ; it is 
probable, although not proved, that they ascend into the dentinal canals. 



F F 2 



i8 4 ATLAS OF HISTOLOGY. 

The capillaries form a dense network in the periphery of the pulp tissue. The 
blood-vessels are ensheathed in endothelial membranes, which form the wall of lym- 
phatics. 

Development of Tooth. 

The first rudiment of the tooth appears at a time when the mucous membrane 
covering the lower jaw is vascular embryonal, or gelatinous tissue, i.e. a network of 
branched embryonal cells ; it is a solid prolongation of the stratified epithelium of the 
surface into the depth of the mucous membrane; this prolongation, somewhat thickened 
at its lower end, is the primary enamel organ. The enamel organ at its deep end becomes 
invaginated by a papillary mass of vascular gelatinous tissue, the embryonal tooth 
papilla, which is entirely derived from the mucous membrane. The primary enamel 
organ is thus gradually converted into the secondary enamel organ, or the enamel cap, 
a caplike covering of the embryonal tooth papilla. 

The part of the gelatinous mucous membrane that immediately surrounds the 
rudiment of the tooth (the secondary enamel organ and the tooth papilla) represents 
the tooth sack. This is a vascular membrane consisting at first of a network of em- 
bryonal cells, but soon very numerous fine fibrils arranged in bundles appear in it. The 
bundles are grouped into lamellae, and these, by anastomosis of neighbouring tra- 
becular, form a sort of meshwork with one another. At this period the tissue of the 
tooth sack is well defined from the mucosa covering it. 

The connection between the enamel organ and the surface epithelium, owing to the 
growth of the tissue of the mucous membrane over the former, is severed at a much 
later stage. 

The tissue of the papilla, as mentioned above, is very vascular, and is composed of 
a network of nucleated cells; it gives origin to the pulp, and by its odontoblasts produces 
the dentin. The odontoblasts make their appearance very early as an epithelial-like 
peripheral stratum of large more or less columnar cells. The odontoblasts elongate at 
their outer or distal extremity, and this is directly converted into the matrix of dentin 
(Waldeyer, Boll, and others). 

Kolliker, Hertz, and others regard the dentin matrix as an excretion of the odontoblasts. 
Previous to its calcification it shows, just like the substance of the odontoblasts, the fine net- 
work of its matrix. 

The outer extremity of the odontoblasts continues to elongate, and the increment is 
again changed into dentin ; and this process continues as long as the dentin increases 
in thickness. The most recently formed dentin remains for a certain time uncalcified, 
and is easily distinguished as such by a well-marked boundary line from the earlier layers 
of dentin, viz. those that have already become calcified. As mentioned above, I cannot 



DEVELOPMENT OF DENTIN. 185 

convince myself of the correctness of the now (since Waldeyer) generally accepted theory 
according to which the peripheral part of the cell-substance of the odontoblasts is trans- 
formed into the matrix of the dentin, while the central part persists as the dentinal fibre; 
from my observations I am on the contrary led to assume that the superficial layer of 
cells, or odontoblasts proper, yields only the dentinal matrix, while the dentinal fibres are 
derived from the processes of the cells of the deeper layer, that is, of the cells wedged in 
between the odontoblasts just referred to. 

Thus, while the continued growth of the outer extremity of the odontoblasts yields 
new layers of dentinal matrix, that of the processes of the deeper layer of cells causes 
the elongation of the dentinal fibres, and enables these to keep pace with the growth of 
the matrix. 

Owing to the growth of the tooth sack over the enamel cap, the connection of tin- 
latter with the surface epithelium becomes gradually severed. The enamel cap being 
a duplicature of stratified epithelium, its innermost cells, viz. those next to the tooth 
papillae, as well as the outermost cells, viz. those next to the tooth sack, arc columnar 
cells, corresponding to the deepest cells of the surface epithelium. Next to the inner 
and outer cells are polyhedral cells, and towards the middle of the enamel cap we find 
more or less flattened epithelial cells. The tooth sack, where it is in contact with the 
upper greater half of the enamel cap, extends as very regular small papillae into the 
outer stratum of the epithelium of the latter. 

The enamel cap is limited both on its inner and outer surface by a membrana 
propria (Huxley, Kolliker). 

The next change that takes place in this enamel cap is a separation into an 
inner and outer membrane, owing to the transformation of the aforesaid middle strata 
of flattened epithelial cells into a transparent tissue, middle membrane ; the matrix of this 
is a honeycomb of membranous structures containing oval flattened nuclei, its meshes 
are relatively larger — much larger than those of the gelatinous tissue of the tooth 
papilla — and contain a hyaline interstitial substance. No vessels are present in this 
middle membrane. 

This change in the middle membrane is due to an accumulation of fluid in the inter- 
stitial substance between the epithelial cells ; hereby these latter are gradually separated 
from one another and compressed into membranous structures, which are connected into 
a honeycomb. It is, therefore, not quite correct to compare this middle membrane of 
honeycombed tissue with the gelatinous connective tissue of the tooth sack or the tooth 
papilla. The inner membrane is composed (a) of a layer of beautiful columnar epi- 
thelial cells in contact with the dentin, or, if this is not formed yet, with the tooth 



l86 ATLAS OF HISTOLOGY. 

papilla. These cells are called the enamel cells (inner epithelium of Kolliker). Each is 

a hexagonal long prism ; their nucleus is situated in the inner part of the cell 

substance : this is a dense reticulum, (b) Outside the layer of enamel cells are one, 

two, or three layers of small polyhedral cells, each with a spherical nucleus : they form 

the stratum intermedium of Hannover. The outer membrane (outer epithelium of 

Kolliker) of the enamel cap is composed of several layers of epithelial cells ; but as 

development proceeds, the middle membrane increasing in thickness at the expense of 

the stratum intermedium of Hannover as well as the cells of the outer membrane, the 

layers of this latter become greatly reduced. Still later, the middle membrane having 

disappeared, the inner and outer membrane are again brought into contact. 

The enamel is formed by the enamel cells of the inner membrane, in the same 
manner as the dentin from the odontoblasts, viz. the distal extremity of the cells, that 
is, the one next the dentin elongates, and this increment is directly converted into 
enamel (Waldeyer, Tomes, Wenzel, and others). Kolliker, Kollman, and others, on 
the other hand, regard the enamel as an excretion of the enamel cells. The enamel 
cells being prismatic, the enamel matrix is accordingly also composed of prismatic 
elements, the above enamel prisms. The increment of the enamel cells and the con- 
version into enamel probably occur successively, and hence the aforesaid transverse 
markings of the enamel prisms receive their ready explanation. The enamel cells, like all 
epithelial cells, being separated from one another by a homogeneous interstitial substance, 
it is clear that the remains of this substance must occur also between the enamel prisms ; 
in the enamel of a developing tooth this interstitial substance is larger in amount than in 
the fully formed organ. It is improbable that nucleated protoplasmic masses are con- 
tained in the interstitial substance of the enamel of a fully formed tooth, as is maintained 
quite recently by Bodecker. 

In the parts adjoining those that are breaking down through caries, the spaces, containing 
this interstitial substance, between the enamel prisms increase, and become filled with granular 
debris. 

A similar relation exists also in caries of dentin, for here also the dentinal canals are enlarged, 
and their contents, dentinal fibres and sheaths, thickened. 

When the most recently formed layer of enamel, the membrane of Huxley (mem- 
brana preformativa of Raschkow), is viewed from the surface, it appears of course to 
consist of closely placed hexagonal sections, these being the enamel prisms seen 
endwise ; each of these sections shows an opaque peripheral and a clear central part. 
This is due to the petrifaction of the prisms taking place first in the periphery, the centre 
remaining for some time transparent. In conformity with this the centre of the distal end 
of the enamel cells retains its soft structure much longer than the periphery, and when 
isolated, these cells present accordingly at that end a shorter or longer process (Tomes). 



DEVELOPMENT OF ENAMEL. l8? 

The cells of the strata intermedium rf ^^ ^ be; for 

formation of part of the above m iddle membrane of the enamel cap, are also utilised for 
the regeneration of enamel cells (Waldeyer). 

By the time the middle membrane disappears, also the stratum intermedium is 
used up, and the ename cells are in contact with the outer membrane or the outer 
epithelium of Kolhker, but separated from it by what appears to be a delicate homo- 
geneous membrane. The cells of thn ™,f~- vi, i- 

a c ., , °' the 0uter epithelium give origin to the cuticle of the 

surface of the enamel, as mentioned on a preceding page. 

The membrana propria above referred to on the inner surface of the enamel cap of 
the earhest stages, can be still recognised as a sharp boundary line between the youna 
enamel and dentin. Later on it entirely disappears. 

The tissue of the tooth sack represents the matrix from which the cement is 
formed ; ,ts structure and function are that of the osteogenetic layer of the periosteum ■ 
the formats of the cement out of that tissue is identical with the subperiostal bone 
development described in Chapter IX. 

Already during the stage of the primary enamel organ of a temporary or milk 
tooth, there is growing out of it a lateral process of epithelial cells; this represents the 
rudiment of the enamel organ of the permanent tooth (Kolliker). The formation of 
this latter takes place on precisely the same plan as that of the temporary tooth 



The knowledge of the structure and development of teeth, as described in the 
foregoing pages, we owe to a great extent to the observations of Purkinje, Schwann 
Henle, Nasmyth, Kolliker, Tomes, Huxley, Owen, Retzius, Hannover, E. Neumann 
Waldeyer, Hertz, Wenzel, Lieberkuhn, Kollmann, and others, and especially to 
Charles Tomes by his numerous researches in the field of comparative anatomy of 
the teeth. 



ss 



ATLAS OF HISTOLOGY 



CHAPTER XXIV. 

SALIVARY GLANDS. 

The salivary glands, according to their structure and secretion, are of three different 

kinds : (a) true salivary glands, as parotid gland of man and mammals, the orbitalis and 

submaxillaris of rabbit ; (6) mixed salivary or muco-salivary glands, as submaxillary 

gland of man and guinea pig ; and (c) true mucous glands, as submaxillary gland of dog 

and cat, sublingual gland of man, orbital gland of cat and dog (Lavdowsky). In all 

instances, however, we find a framework consisting of a capsule of fibrous-connective 

tissue, and in connection with this thinner and thicker septa, which subdivide the 

gland substance into lobes and lobules. This connective tissue is composed of bundles 

of fibrous-connective tissue arranged more or less in lamellae, and between these are 

the flattened more or less branched connective-tissue cells. Into the interior of the 

lobule penetrate only small bundles of fibrous-connective tissue, but chiefly the con- 

nective-tissue cells. The small ducts within the lobules are always surrounded by a 

conspicuous amount of fibrous-connective tissue ; the large or lobar ducts run within 

the connective tissue forming the interlobar septa. There are found in all parts of the 

connective tissue, both inter- and intralobular, isolated or small groups of migratory cells 

(Boll, Lavdowsky). The connective-tissue framework is at the same time the support of 

the blood-vessels, lymphatics, nerves and ganglia. 

The salivary glands of all categories have the same kind of ducts : beginning with 
the chief duct down to the lobar, and intralobular duct and its finest ramifications, we 
find in all corresponding sections the same structure. The lobar ducts, as the largest 
microscopical ducts, possess a relatively large lumen, lined by a single layer of beautiful 
columnar epithelial cells. Each of these consists of a finely striated protoplasm, owing 
to its containing an intracellular network of a pre-eminently longitudinal arrangement 
(Klein) ; the outer part of the cell contains the oval nucleus with its intranuclear network. 
Then follows a delicate membrane, on which the epithelium rests, and this is strengthened 
by fibrous-connective tissue, varying in amount according to the size of the duct. In the 
largest ducts, including the chief duct, there are unstriped muscle cells included in the wall. 

The intralobular ducts (salivary tubes of Pfliiger) differ from the former, not 
merely in their size and position, and in the thickness of their wall, but chiefly by their 
structure. Each of them possesses a relatively small lumen, this is lined by a single layer 



EPITHELIUM OF DUCTS OF SALIVARY GLANDS 189 

of columnar epithelial cells, the substance of which appears to consist of closely placed 
relatively thick longitudinal rods (Kolliker). When examined more carefully, it can 
be ascertained, however, that these rods anastomose with one another by few short 
lateral branchlets, so as to form a network (Klein). Each cell has an oval or spherical 
nucleus situated about the middle or a little beside the latter. The striation is generally 
more distinct in the inner part of the cell substance than in the outer, owing to the above 
network being closer and more uniform in the latter than in the former. The epithelium 
is situated on a thin membrane containing oval flattened nuclei at more or less regular 
intervals, probably an endothelial membrane. The outline of the intralobular ducts 
is never smooth, but irregular and wavy, owing to the irregularity in size (height) of the 
epithelium at different places. 

The large intralobular ducts branch into the smaller ones, and these are ultimately 
connected with, and pass into, the proper gland substance or alveoli. But before doing so, 
they undergo a change in their structure, and assume special characters by which they 
are easily distinguished, the terminal or intermediary part (v. Ebner). This latter varies 
in length in different salivary glands, being longer in the human submaxillary gland than in 
that of dog. It is much narrower than the intralobular duct, its lumen is smaller, and its 
epithelium either a single layer of polyhedral transparent cells, each with a spherical 
nucleus, as in dog's submaxillary gland, or it is a layer of flattened cells, each with a 
flattened nucleus, as in the submaxillary gland of man. The intermediary part is often 
branched before it passes into the alveoli (Grot). 

The proper gland substance is in all salivary glands made up of branched tubes 
of varying lengths, much convoluted, and of a wavy appearance (Grot). This 
type of gland is called compound tubular. The tubes are closely placed against 
one another, and extending with their branches and convolutions in all different 
directions, it is natural that, in any section through the gland, we should find them 
cut under very different angles : transversely, obliquely, and longitudinally. Between 
the individual tubes or alveoli are capillary blood-vessels, lymphatic spaces, and the 
connective tissue mentioned above. This latter varies, however, hi different glands, 
and determines the closeness of the position of the alveoli ; thus in the submaxillary 
gland of man there is considerably more interalveolar connective tissue than in the 
dog, and therefore the alveoli in the former instance are less closely placed than in the 
latter. 

The membrana propria of the alveoli appears as a delicate homogeneous membrane 
containing from place to place flattened nuclei, being in reality made up of richly 
branched flattened cells connected with each other (Henle, Heidcnhain, Boll and others). 
Their processes are either fine and threadlike or broad and membranous, and the 



G G 



ATLAS OF HISTOLOGY. 
network, adapting itself to the curvature of the alveoli, possesses in a given portion of 
the latter a basket-shaped arrangement. 

In connection with these cells are minute membranous or filamentous septa, passing 
inwards between the epithelial cells lining the alveoli (Boll) ; they are lost in the cement 
substance between the epithelial cells. 

This cement substance corresponds to the capillary ducts described by some writers 
in the salivary and other glands (Saviotti, Langhans, Schwalbe, Ewald, Boll, Grot, and 
others). According to v. Ebner they are merely clefts, without any special wall, 
between the epithelial cells. Hering also denies their existence as special canals. 
Latschenberger takes the same view with reference to the pancreas. 

The nature of the lumen and the epithelium lining it determines the character of 

the gland. It is this : 

a) In the true salivary gland: the lumen of the alveoli is small, the epithelial 
cells form a single layer of columnar or short columnar cells, each with a spherical 
nucleus situated in the peripheral part of the cell. The substance of this latter appears 
'granular/ but is in reality a very dense network. Also the nucleus contains an 
intranuclear network. During secretion the lumen of the alveoli becomes still smaller, 
while the lining cells become broader than during rest. 

In the parotid gland, in the greater portion of the lobules of the submaxillary 
gland of man and guinea pig, in the submaxillary and orbital glands of rabbit, the alveoli 
show the structure just described. 

R. Heidenhain observed that the alveoli of the parotis of rabbit alter considerably 
their aspect after the stimulation of their sympathetic nerve. While after the stimula- 
tion of the cerebral nerve the cells lining the alveoli do not show any change from the 
resting state, after the stimulation of the sympathetic the cells become very much 
diminished in size and their contents very opaque. A similar change is observed also 

in the parotis of dog. 

6) In the true mucous glands ; the alveoli are considerably larger than in the 
former case, not only on account of the greater length of the lining epithelium but 
chiefly owing to the much greater lumen. The cells are of two kinds : 

i) The mucous cells (Heidenhain) or central cells line the lumen, and are trans- 
parent columnar cells in all respects resembling goblet cells, as mentioned in Chapter 
II. ; with their pointed extremity they are applied to the membrana propria, but so as to 
be imbricated with each other (Kblliker). The nucleus is much compressed and next to the 
membrana propria. The cell substance, as is generally the case in goblet cells, is a deli- 
cate network, the meshes of which contain in the resting state a transparent substance : 
this is the mucigen of Heidenhain. When secreting this substance is transformed into 



STRUCTURE OF SUBMAXILLARY GLAND. 



mucin, and as such stains deeply fa in hfematoxylin . Qn ^ . 

water ,t greatly .creases in bulk, and hence produces a „ increase J'* 



enlaced, and the cell therefore , ooks more t _. ~ " ~ 

in the inner portion of the cell possesses a I™,*:* a- i ^ucmum 

, h „ x, J; . Possesses a longitud.nal arrangement (Klein), and hence 

the cell substance appears as if longitudinally striated 

2 ) The crescents of Gianuzzi represent semilunar groups of parietal -granular' cells 
apphed from place to pace to the outer surface of the mucous cells but inside the 
membrana propria (Heidenhain). The parietal cells are small polyhedral cells, eac 
w.th a spherical nucleus (He.denhain, Asp). The substance of these cel.s appear 
granular owing to its being composed of a very dense reticulum with very little Iter 
stitial substance in its meshes. 

During secretion also the crescents become enlarged (Lavdowsky, Klein), and 
the alveolus as a whole ,s larger, although its lumen is somewhat reduced in size In an 
exhausted gland (by electric stimulation or chemical action), the transparent mucous cells 
d,sappear as such, the alveoli are much smaller, being now lined only with poly 
hcdral or short columnar < granular ' cells similar to the parietal cells. Heidenhain Boll 
and Lavdowski conclude from this that the mucous cells have become destroyed and 
that the parietal cells have taken their place, probably in consequence of a process of 
new formation. Ewald, however, explains the same appearance by assuming that the 
mucous cells, in consequence of the exhaustion, have lost all their mucous contents and 
have shrunk into small 'granular' cells. Ranvier, v. Eberth, and others also question the 
accuracy of Heidenhain's interpretation. Under ordinary conditions of secretion, how- 
ever, the mucous cells do not become destroyed nor ever alter their appearances more 
than is indicated above (Klein), viz. a reticulum with transparent mucigen in its meshes, 
is found in the resting state, while during secretion its meshes become enlarged owing 
to the contents having swollen up and transformed into mucin. 

Judging by analogy (see below) the mucous cells when exhausted very probably 
become much smaller, their network being closer and containing in its meshes much less 
interstitial substance, and hence the cells present a 'granular ' aspect. 

This is borne out also by experiment, for through Heidenhain, Pfliiger, Lavdowsky, Ewald, and 
others it is known that the saliva secreted by the exhausted gland is watery, while in a previous 
stage it is mucus. The explanation of this would then seem to be this: when the mucous cells have 
discharged all their mucin, that is, when their substance has become 'granular,' like that of the cells 
of true salivary gland, also their secretion becomes similar to that of the latter, viz. watery. 

In the submaxillary gland of young animals all transitional stages are met with 
between small alveoli with small lumen lined only with small 'granular' cells, and 

C C 2 



JQ3 ATLAS OF HISTOLOGY. 

alveoli somewhat larger and lined either partly with mucous cells, partly with granular 
cells, or altogether with mucous cells to which are applied from place to place groups 

of 'granular' cells. 

Such is the nature of the alveoli in the submaxillary and orbital gland of dog, 

and in the sublingual gland of man. 

c) In the mixed or muco-salivary glands, as in the human submaxillary gland and 
in that of the guinea pig, we find amongst lobules of true salivary gland smaller lobules 
of mucous gland, the structure of the alveoli of which is similar to that of the sub- 
maxillary gland of the dog, viz. a large lumen, lined with mucous cells, and outside 
these from place to place crescents of parietal cells. But even in one and the same 
lobule we may find the larger part composed of true salivary gland structure, while a 
small part is represented by mucous gland. More than that, in the submaxillary gland 
of man and guinea pig, we meet with alveoli of the structure of mucous gland de- 
scribed just now, directly continuous with alveoli that are smaller, have a smaller 
lumen, and are lined only with 'granular 0/&,that is, alveoli identical with true salivary 
gland-structure (Boll, Klein). 

Nussbaum maintained that by the aid of osmic acid it is possible to show that in 
the submaxillary gland of rabbit the cells lining the alveoli immediately adjoining the 
intermediary part of the duct, above described, possess a different character from the 
cells of other parts of the alveoli, and that the former are concerned in the secretion of the 
salivary ' ferment.' Langley denies the correctness of both the morphological as well as 
the physiological part of this assertion. 

Bermann describes in the submaxillary gland of man, rabbit, dog, bat, &c, in connec- 
tion with a large branch of the ductus Whartonianius, a compound tubular mucous gland 
whose structure is altogether different from the rest of the gland. 



The alveoli of all salivary glands, like those of other glands, are surrounded by a 
dense network of capillary blood-vessels, and between them and the alveoli we find also 
lymph spaces and clefts surrounding the greater part of the circumference of the alveoli 
(Boll). The lymphatic vessels taking up these spaces lie in the interlobular septa, where 
they form a plexus. 

The nerve branches are composed of medullated nerve fibres, and form a plexus in 
the interlobular connective tissue. In connection with this plexus are larger or smaller 
ganglia; in some places they form spherical or oval enlargements, in others they are 



NERVES OF SALIVARY GLANDS. 193 

represented by smaller or larger chains of ganglion cells within a nerve branch. Their 
structure has been described and figured in a former chapter (see figure 1 1. Plate XXI I.). 
Most of these ganglion cells are unipolar, and ensheathed in a special capsule. 

According to Prliiger, the nerve fibres coming off from this plexus remain medullated 
until their termination is reached, viz. just before they enter the intralobular ducts ( Pllucrer's 
salivary tubes) and alveoli. Then each nerve fibre loses its medullary sheath, and its axis- 
cylinder, composed of minute fibrils, becomes directly connected with the cell substance 
of the epithelium of those ducts. The nerve fibres for the alveoli remain medullated 
until the membrana propria is reached, they are also in direct continuity with the lining 
cells. Thus all the epithelial cells are real terminations of nerve fibres ; and during 
regeneration they are direct outgrowths of the nervous elements. 

Prliiger also mentions isolated multipolar ganglion cells (Krause) between alveoli, 
by their intervention a connection is occasionally established between nerve fibres and 
epithelial cells. 

These assertions of Pfliiger have received a certain amount of support in the observa- 
tions of Kupffer on the termination of nerves in the salivary gland of periplaneta orien- 
talis. Kupffer saw here a plexus of fine nerve fibres surrounding the alveoli of the 
gland ; from it pass minute fibres which enter the epithelial cells themselves, in whose 
reticular substance they terminate. 

But, on the other hand, with regard to the nerve distribution in the salivary glands 
of man and the other mammals, the correctness of Pfluger's assertions has been questioned 
or altogether denied by all who have investigated this subject. 



I94 ATLAS OF HISTOLOGY. 



CHAPTER XXV. 

ORAL CAVITY, PHARYNX, (ESOPHAGUS, AND STOMACH. 

i. Tui- mucous membrane lining the mouth and palate is, in man and mammals, covered 
with a thick stratified pavement epithelium. The arrangement of this, its minute 
structure, and the occurrence of prickle cells have been described in Chapter II. The 
deepest layer of the epithelium is composed of more or less columnar epithelial cells, each 
with an oval nucleus ; then follow several layers of polyhedral cells with a spherical nucleus ; 
nearer to the surface the cells and their nucleus become more flattened, and on the 
surface itself the cells are transformed into scales, each with a flattened circular nucleus. 

In the mucous membrane of mouth of man the flattened cells of the most superficial layers 
possess each a flattened nucleus, except in the transitional part of the lip, that is, the red part 
seen even when the lips are touching ; here many of the superficial cells are horny 
scales without a distinct nucleus, more or less closely packed together. In mammals we find in 
many instances the superficial cells with only traces of nuclei in them, and more or less fused into 
a bright horny stratum. 

Underneath the epithelium is a basement membrane, a delicate endothelial membrane. 
Then follows the mucosa, a dense connective-tissue membrane, chiefly composed of bundles 
of fibrous-connective tissue, arranged as smaller or larger trabecular crossing each other in 
various directions. The interfascicular lymph spaces, containing the connective-tissue 
corpuscles and the networks of elastic fibrils attached to the surface of the trabecular, 
have been mentioned on several previous occasions. The thickness and firmness of the 
mucosa varies in different parts ; thus, for instance, the mucosa is much thicker on the 
lips, angle of mouth, and buccal region than at the bottom of the mouth, soft palate, 
and palatine arches, and it is much firmer on the gums and hard palate than anywhere 
else, owing to the tendinous nature of its connective tissue, and its intimate fusion with 
the fibrous tissue of the subjacent periosteum. In all instances, however, the surface of 
the mucosa is raised as conical or cylindrical papillae, extending into the epithelium. 
The tissue of the papillae is rich in connective-tissue cells. The epithelium and sub- 
epithelial basement membrane adapt themselves to the unevenness thus produced ; the 
masses of epithelium filling the grooves and pits between the papillae have been men- 
tioned (Chapter II.) as interpapillary processes. 

About the entrance of the mouth are found occasionally, in new-born children, papilla? that pro- 



STRUCTURE OF MUCOUS MEMBRANE OF ORAL CAVITY. 195 

ject freely above the general surface of the epithelium, and are covered with a continuation of the 
general epithelium similar to the papillae filiformes of the tongue (Klein). 

The deeper parts of the tissue of the mucosa pass insensibly into the loose connec- 
tive tissue which constitutes the submucosa or the submucous tissue. In this the 
trabecule or groups of bundles do not cross so repeatedly, but possess a more or less 
distinct lamellar arrangement, and are separated by large interfascicular lymph spaces. 

The submucous tissue contains masses of fat cells, the large branches of vessels 
and nerves, the glands and striped muscle, and extending outwards, forms a continuity 
with the connective tissue of the surrounding organs, as muscle, periosteum, skin, &c. 

As has been mentioned in a former chapter, the mucosa of the tonsils and soft palate contains 
masses of adenoid tissue, which in the former assumes the shape of lymph follicles. In some places 
the adenoid tissue with its lymph corpuscles by active growth encroaches on the epithelium. 

The glands of the mucous membrane are mucous glands, and very conspicuous by 
their large size. The largest are found in the lower lip and soft palate. Each gland 
consists of the duct and the secreting part proper. The former is a tube passing 
in a vertical or, more usually, oblique direction from the submucous tissue (the gland 
proper) through the mucosa, and opens on the free surface of the epithelium with a funnel- 
shaped ' mouth.' The duct is limited by a membrana propria, containing oval flattened 
nuclei from place to place, being probably in all instances an endothelial membrane. It is a 
direct continuation of the subepithelial basement membrane. The duct possesses a 
large lumen, and this is in man lined with a single layer of beautiful columnar epithelial 
cells, each with an oval nucleus. The substance of these cells is longitudinally striated, 
containing an intracellular network of fibrils of a pre-eminently longitudinal direction. 
The nucleus contains also a reticulum. At the mouth the stratified epithelium of the 
surface passes, in an attenuated form, a short distance into the duct, but is soon 
replaced by the above columnar epithelium. In mammals the epithelium remains, 
however, stratified, being composed of two or three layers of flattened cells, until the 
deep part of the duct is reached, where it is composed of a single layer of poly- 
hedral cells. 

The oral cavity, the pharynx and oesophagus of batrachiae, are lined with ciliated columnar 
epithelium. The posterior surface of the soft palate and uvula are in the human embryo covered 
with laminated columnar epithelium, of which the most superficial cells arc ciliated, but in the 
adult the epithelium is stratified pavement epithelium (Klein), as in other parts of the oral mucous 
membrane. The epithelium lining the ducts and indeed of the whole gland is developed as a 
continuation of the epithelium of the free surface ; this explains how sometimes also in the adult 
the epithelium lining the first part of the duct is ciliated (Klein). 

In the submucous tissue the duct branches in several branches, each of which 
having become slightly narrower, and its epithelium flattened, generally becomes again 
somewhat enlarged, as infundibulum, where it passes into the secreting part. This consists 



ig6 ATLAS OF HISTOLOGY. 

of tubes much convoluted, and possessed of shorter or longer lateral branches ; each of these 
possesses a relatively large lumen ; so that the secreting part of the gland is a compound 
tubular gland (Puky Akos). The mucous glands of all parts of the cavity of the mouth 
and pharynx are compound tubular glands, identical in structure (v. Ebner, Teraszkievicz, 
Podwisotzky, and others). They vary in size according to the number and length of the 

tubes. 

The wall of both the infundibulum and gland tubes is a membrana propria, 

composed oi a network of branched, flattened cells, each with a flattened nucleus. 

From these cells and their processes come off thin membranous and filamentous septa, 

which pass in between the epithelial cells of the gland. And this structure, viz. a 

membrana propria composed of branched, flattened cells, and membranous or filamentous 

septa coming off from the former and passing into the cement substance of the epithelium 

lining the gland, repeats itself in all glands , no matter what their function, arrangement, 

or structure (Boll, Schwalbe, v. Ebner, Watney, and others). The epithelium lining the 

lumen is a single layer of thin columnar epithelial cells. These are similar in structure to 

the mucous cells lining the alveoli of the submaxillary gland of dog, viz. transparent 

cells composed of an intracellular network, with relatively wide meshes. The nucleus 

is more or less flattened and pressed against the membrana propria. During rest the 

meshes of the intracellular network contain a transparent mucigen, which during 

secretion changes into mucin. When exhausted the network is closer, there being less 

interstitial substance in its meshes, and the cells appear therefore shorter and more 

' granular ;' in this period we find their nucleus nearly spherical. Similar are the epithelial 

cells lining the alveoli when not yet fully developed, viz. short and ( granular ;' the nucleus 

is at the same time not flattened and pressed against the membrana propria, but spherical 

and at a little distance from the latter ; the lumen of the alveoli is very minute, and 

hence their diameter is much smaller than when fully developed. 

In some localities there is outside the lining cells of the alveoli an indication of 
crescents similar to those described of the submaxillary gland of dog, viz. a semi- 
lunar group of small 'granular' cells, each with a spherical nucleus. In the case of the 
mucous glands the crescents are very thin and scarce. 

The transition of the epithelium of the duct into the mucous cells of the infundibulum 
is more or less sudden, the flat or polyhedral cells at the end of the duct, which may be con- 
veniently called the intermediary part, become sooner or later longer and more transparent. 
This change does not occur simultaneously at all points of the circumference, for we see 
occasionally that while on one side the epithelium has already undergone the above 
alteration, it remains unchanged for some distance longer on the other side of the lumen 



of the gland tube. 



VESSELS IN MUCOUS MEMBRANE OF MOUTH. , Q ; 

Toe Blood-Vessels ; the arterial trunks give off branches which pass in an oblique 
direction through the mucosa, in the superficial parts of which they dissolve into a 
network of capillaries extending in a horizontal direction. Single or double loops of 
capillaries of this network occupy the papillae. The veins proceeding from the super- 
ficial capillary network form a plexus the efferent branches of which pass into the 
submucous tissue, where they join the large venous trunks. Lymph follicles, striped 
muscle, fat tissue, and mucous glands possess their own system of blood-vessels, 
consisting of afferent arterioles, a dense network of capillaries, and efferent veins. The 
nature of the capillary network differs in these different tissues ; its characters in lymph 
follicles, in striped muscle and fat, have been described in previous chapters ; as for the 
mucous glands the capillaries form a uniform network surrounding the alveoli similar to 
what is the case in the salivary glands. 

The lymphatics ; these are arranged, according to Teichmann, as a superficial net- 
work of tubular capillary vessels belonging to the surface of the mucosa : from it ascend 
blind or looplike branches for the papillae. Lymphatic vessels with valves pass from 
this network, and penetrate into the depths and join the deep network of large trunks 
belonging to the submucous tissue. The relation between the lymphatic capillaries 
and the lymph-canalicular system of the mucosa, as well as that of the interfascicular 
spaces and sinuses of the submucous tissue to the lymphatics of the latter, has been 
mentioned on a previous occasion. 

The nerves ; they are distributed as a subepithelial plexus of fine bundles of nerve 
fibres, as a subepithelial network of fine elementary fibrils, and finally as intraepithelial 
fibrils, which probably terminate as a network (Elin), described in Chapter XVII I. 
It remains to be added here, that Krause observed end bulbs in the papilla? of the 
lips of the mouth of many mammals ; Kolliker and Gerlach found in the same 
places, viz. papillae of lips, tactile corpuscles similar to Meissner's corpuscles in the 



skin. 



2. The tongue. — The mucous membrane of the tongue differs in structure in 
several respects from that of other parts ; on the dorsum of the tongue it is very thin 
and firmly connected with the muscular tissue, but at the root it is much thicker, 
looser, and placed in numerous complex permanent folds. The epithcliu 
the surface of the tongue is everywhere a stratified pavement epithelium, it 
thinner at the lower surface than in the other parts. The freely projecting papilke 
nliformes and fungiformes, including the papilla? circumvallata?, are covered with the 
same stratified pavement epithelium as other parts, with the difference that, owing to 
tne erect position of the papillae and to the epithelium following the surface of these 



m covering 

o 



is mucli 



„ ATLAS OF HISTOLOGY. 

1 9« 

latter, the direction of the epithelial cells of the different layers over the papillae 

themselves is nearly at right angles with that of the parts between. 

The papillae filiformes are single or compound, in the latter instance two, three, or 

more papillae project from a common large papilla ; but each papilla, whether single or 

compound, includes, as a rule, minute papillary projections of the mucosa, forming the 
matrix of the papilla, into the epithelium covering it, similar to what is the case in other 
parts of the mucous membrane of the oral cavity. The epithelial cells of the apex of 
the papillae are much flattened, and in the adult we meet with small groups of them 
forming filamentous horny prolongations. In the papillae filiformes of mammals the 
superficial strata of the epithelium are often composed of horny scales closely packed 

together. 

The papillae fungiformes are covered with beautiful stratified pavement epithelium, 

into which project larger or smaller secondary papillae. 

The mucosa forming the matrix of the papillae is of the same connective-tissue 
nature as that of other regions of the oral cavity, except in the fungiform papillae, 
especially in the large ones forming the centre of a circumvallate papilla, it contains 
numerous nerve branches composed of medullated nerve fibres. 

The distribution of blood-vessels and lymphatics does not differ from that of other 
parts, except that the papillae have each a single or multiple loop of capillaries, according 
as they are single or compound. In the fungiform papillae the blood capillaries form a 
very beautiful network. 

In the root of the tongue the mucous membrane is loose and contains numerous 
secreting glands, lymphatic follicles, and diffuse adenoid tissue. 

The former, viz. secreting glands, are buried between bundles of striped muscle 
fibres, their ducts pass through the mucosa and open generally in the grooves, pits or 
crypts between or in the folds or knoblike prominences, with which the surface is beset ; 
the lymphatic follicles are closely aggregated in the mucosa and extend into the 
epithelium of the surface as diffuse adenoid tissue. Their relation to the mucosa and 
the epithelium is the same as that described of the tonsils in a former chapter, viz. the 
folds or larger and smaller knoblike papillae and crypts of the mucous membrane are 
chiefly caused by the presence in their wall of the above lymph- follicles and diffuse 
adenoid tissue (Kolliker, Huxley). As in the tonsils, so also at the root of the tongue, 
the adenoid tissue of the mucosa gradually encroaches on the epithelium, this latter 
becoming filled with lymph-corpuscles and reticulum. The lymph- corpuscles may be 
traced in many places up to the free surface. There is little doubt that the so-called 
salivary or mucous corpuscles, found in the mucus and saliva taken from the cavity of 
the mouth, are lymph-corpuscles that have originally belonged to the adenoid tissue 



STRUCTURE OF TASTE GOBLETS. , 99 

of the tonsils, root of tongue, or soft palate, and have made their escape through the 
epithelium of these organs. Like other lymph corpuscles they exhibit the power of 
amoeboid movement. Under the influence of water they swell up into spherical 
corpuscles, containing numerous granules that show very lively Brownian molecular 
movement. In this latter aspect they generally present themselves in the saliva and 
mucus taken from the oral cavity. 

Taste organs.— The circumvallate papillae, many fungiform papillx, and certain 
permanent folds at the side of the root of the tongue of man and mammals are distin- 
guished by the presence of taste goblets, discovered by Schwalbe and Loven. 

The description of their structure, as given by Schwalbe, is in its chief points still 
generally accepted. 

Each taste goblet is a goblet-shaped or elliptical organ, embedded vertically in the 
stratified epithelium in such a manner that one end of it is on the free surface, the other 
touches the tissue of the mucosa, and the sides are bordered by the epithelium. This 
latter forms a special covering for the taste goblet by a layer of flattened epithelial cells, 
imbricated one with the other, and each possessed of a flattened circular nucleus. 
The goblet itself contains : (a) the peripheral or tegmental cells (Schwalbe, Loven), 
which by their peculiar arrangement determine the shape of the goblet. They are 
elongated, spindle-shaped, slightly flattened cells, each with a flattened circular or oval 
nucleus; they are occasionally branched (Schwalbe). (6) The central cells, or taste 
cells (Engelmann) : these are slender, spindle-shaped or staff-shaped cells, each with a 
spherical nucleus in about the middle of the cell. Both extremities are filamentous ; 
the outer extremity projects as a fine hairlike process a short distance beyond the 
free opening of the goblet, while the inner extremity is directed towards the mucosa, 
and is in some instances branched in two fine processes (Engelmann). Great numbers 
of nerves are found in the mucosa near the taste goblets, and, according to Engelmann, 
and especially Honigschmied, fine nerve fibrils are directly connected with the taste cells. 
The taste goblets have a wide distribution in man and mammals. They are found 
in rows, at the base of the circumvallate papillae, at the base of many fungiform 
papillae, in the permanent folds known under the name of papilla; foliata: (Weber), 
and occurring at the side of the human tongue and the tongue of many mammals, 
especially in rabbit, where they form on each side a very conspicuous organ. In the 
papilla foliata the taste goblets occur in three or four closely placed rows at the base 
of the fold. v. Wyss and Engelmann minutely described them in the papilla foliata 
of rabbit, v. Ajtai in the papilla foliata of man, Honigschmied showed their distri- 
bution in the papillae circumvallatae and foliatae of many mammals, Krause and Hoff- 
mann observed them in the fungiform papillae of man, and the latter author described 



H H 2 



20O 



ATLAS OF HISTOLOGY. 

taste goblets also in some papilla of the soft palate. Isolated taste goblets occur, 
according to the same observer, also on the summit of some fungiform and circumvallate 

papillae of man. 

The parts oi tongue that contain taste goblets, especially the circumvallate papillae 
and the papillae foliate, are also distinguished by large saccular lymphatic capillaries 
embedded in the mucosa; each fold of the papillae foliate contains in the centre a large 
lymphatic sinus, the wall of which is a single layer of endothelium, and which is 
connected with the superficial plexus of the lymphatics of the mucosa. 

The secreting glands of the root of the tongue are of two kinds, serous glands and 
mucous glands (v. Ebner). The latter differ in no way from the mucous glands of 
other parts of the oral cavity, as described on a previous page. Their ducts are occa- 
sionally (in man) lined with ciliated epithelium (v. Ebner). The mucous glands occur 
only at some distance from the parts that contain taste goblets. The glands present in 
the apex and marginal parts of the tongue (Blandin, Nuhn, Wardt) are mucous glands. 
The serous glands differ in position and structure from the mucous glands; they 
occur always in the parts that contain taste goblets (v. Ebner), and their ducts open 
with a funnel-shaped mouth in the grooves or pits lined by the taste goblets (papillae 
circumvallatDe and papillae foliatae). 

The thick stratified pavement epithelium of the surface is continued into the mouth 
of the duct, but soon becomes thinner, being composed of a limited number of layers of 
polygonal cells ; in the deeper parts of the duct the epithelium is a single layer of 

columnar cells. 

The duct branches in several minute ducts, each of which is, just as in the case of 
the mucous glands, connected with a wavy and convoluted branched tube, alveolus ; the 
branches are all closely pressed together, and hence in any section through the gland 
we meet with tubes cut under different angles : transversely, obliquely, and longitudinally. 
The lumen of the alveoli is very small, in many cases not at all distinct, or only just 
indicated as a fine canal. Their epithelium is a single layer of more or less columnar 
cells, each with a spherical nucleus, similar to the cells lining the alveoli of true sali- 
vary glands. The cell substance looks like granular protoplasm, but is in reality a 
dense network, as described of the cells of the true salivary glands. The membrana 
propria of the alveoli is formed, as in other glands, by a network of flattened and 
branched nucleated cells (v. Ebner). It is very probable that the secretion of the 
serous glands is, like saliva, of a watery nature, and owing to the above-mentioned 
distribution of the glands and their ducts, it (the secretion) is poured out directly over 
the parts containing the taste goblets. This naturally greatly assists the rapid and 
efficient distribution of the substances, to be tasted, over the taste area, an effect that 



DISTRIBUTION OF NERVES AND GANGLIA IN THE TONGUE. 201 

could not be easily achieved if the secretion were viscid, viz. if it were that of a mucous 
gland (v. Ebner). 

According to Krause and Kolliker, the nerves of the papillae of the tongue contain 
end bulbs, and according to Geber also tactile corpuscles of Meissner, This latter can 
be fully confirmed. 

In connection with the nerve trunks situated in the intermuscular connective 
tissue, especially in the parts containing secreting glands, we meet with smaller or larger 
ganglia (Remak). They possess the same structure as those of the submaxillary gland, 
and it is quite probable from their distribution that also in the tongue they bear an 
intimate relation to the glands. 

3. The pharynx. — The mucous membrane lining the lower greater section of the 
pharynx is similar to that of the oral cavity as regards the epithelium, the structure 
of the papillae, of the mucosa and submucosa, the mucous glands in the latter, and 
the distribution of blood-vessels and lymphatics. 

In the upper section the epithelium is like that of the respiratory organs, viz. 
stratified columnar epithelium, the most superficial cells being ciliated. The mucosa is 
possessed of numerous folds and crypts, the wall of which contains lymphatic follicles and 
diffuse adenoid tissue similar to what is the case at the root of the tongue and the tonsils, 
and hence the designation of pharyngeal tonsil (Luschka). The pits and crypts are 
lined by beautiful ciliated columnar epithelium (Luschka). According to Ganghofner the 
epithelium lining the mucous membrane of the bursa pharyngis of children, especially 
the part that he designates as recessus pharyngis medius, is in some places composed of 
ciliated columnar cells, in others, as on the folds of the mucosa, of stratified pavement 
epithelium. This latter epithelium occurs also as small islands amongst large continents 
of cylindrical ciliated epithelium. 

4. The (esophagus. — The cesophagus of man and mammals is lined with stratified 
pavement epithelium of the same nature as that of the oral cavity and pharynx ; its 
(epithelium) thickness is much greater in man than in mammals. The mucosa is a dense 
connective-tissue membrane projecting into the epithelium as longer or shorter conical or 
cylindrical papillae. These are largest in the human cesophagus. The mucosa is separated 
from the loose submucous tissue by unstriped muscle cells, running in a longitudinal 
direction, and arranged in larger or smaller bundles — muscularis mucosae. In the 
beginning of the cesophagus, the bundles are small and separated by a great amount of 
connective tissue, further down they become closer, until they form a continuous layer, 
whose thickness increases towards the lower parts. The thickness of the mucosa, and 



ATLAS OF HISTOLOGY. 

that of the muscularis mucosa, vary in different animals, it is inferior in man to that 
in carnivorous animals. In the dog the muscularis mucosa, is very thick, and its 
bundles are connected with one another in a plexus. 

The submucous tissue contains the mucous glands ; they and their ducts are of the 
same nature as those of the oral cavity. The glands are scarce in the oesophagus of 
man, in carnivorous animals they are well developed, forming in the lower half of the 
organ a continuous stratum. In carnivorous animals the cells lining the gland tubes are 
mucous cells, showing the same structure and changes during rest, secretion and exhaus- 
tion, as described of those of the mucous glands of the mouth. The reticulated nature of 
the cell substance of the gland tubes is shown with great distinctness in the dog. The 
epithelial cells of the glands in man are beautifully columnar, and show the same changes 
during rest, secretion, and exhaustion, as mentioned previously. The ducts pass through 
the muscularis mucosae and the mucosa in a vertical or oblique direction, and open with 
a narrow mouth on the free surface. The epithelium of the ducts shows the same difference 
in man and mammals as in the glands of the oral cavity. 

Outside the submucous tissue is the external muscle coat, consisting in man of an 
inner circular and an outer longitudinal coat. The former is thicker than the latter in 
all parts, except the upper fourth. Outside this is a longitudinal thin membrane of 
fibrous-connective tissue. The trabecular of the submucous tissue are continuous with 
the connective tissue separating the muscle bundles of the muscle coats. In man the 
external muscle coat consists of striped fibres in the upper half of the first fourth, 
in the second half small bundles of unstriped muscle cells appear gradually amongst the 
former, their number increases rapidly, so that in about the middle of the oesophagus 
the striped fibres are altogether replaced by the unstriped ones. 

In mammals the striped muscle fibres, more or less separated by bundles of unstriped cells, 
remain to the cardia. In carnivorous animals, the external muscle coat is in many places 
composed of more than two layers, the muscle bundles having mostly a course more or less spiral 
around the long axis of the oesophagus. 

The blood-vessels have a similar distribution as in the pharynx, viz. from the 
arterial trunks situated in the submucous tissue proceed branches which in the upper 
part of the mucosa form a network of capillaries, these give off loops for the papillae. 
The venous branches pass the reverse way, viz. from the superficial network of capil- 
laries through the tissue of the mucosa, into the venous trunks of the submucosa. The 
Hands of the latter tissue, the muscularis mucosae, and the external muscle coat, 
possess their own vascular system. 

The lymphatics form a plexus of capillaries belonging to the surf?ce of the mucosa 
(Teichmann) ; from them proceed the lymphatics of the papillae, each of these possessing 



NERVES AND GANGLIA IN THE (ESOPHAGUS. 203 

a single c^ecal vessel or a loop. The plexus of lymphatics of the mucosa is in commu- 
nication with a plexus of large tubular vessels belonging to the submucosa (Teichmann). 
In connection with the submucous lymphatics, in the cesophagus as well as in the 
pharynx, are special lymphatic vessels and sinuses belonging to the mucous glands 
(Kidd). 

The plexus of large nerve trunks surrounding the cesophagus includes larger and 
smaller ganglia (Remak). The nerve-branches that enter the cesophagus form a dense 
plexus of smaller or larger bundles between the circular and longitudinal layer of the 
external muscle coat. In these nerve branches we meet with isolated or chains of 
ganglion cells (Klein). Each of these is enclosed in a capsule. The submucous tissue 
contains another plexus of nerves, connected with the former plexus, and also in this may 
be met with occasionally isolated ganglion cells (Klein). 

5. The Stomach. — The epithelium covering the free surface of the gastric mucous 
membrane is a single layer of columnar epithelial cells ; in many places the cells are 
mucus-secreting goblet cells (Strieker, F. E. Schultze, Klein, Watney, and others); this 
is especially the case during digestion, when all cells are secreting mucus. The nature 
of the intracellular network in the ordinary epithelial cells, and in the goblet cells, 
and the relation of the ordinary epithelial cells to the goblet cells, have been fully 
described in Chapter II. The lower or inner portion of the epithelial cells, containing 
the oval nucleus, remains always the same, viz. composed of a dense network, even 
while the upper part becomes changed into the mucus-secreting goblet. The epithelium 
of the surface is continued into the ducts of the gastric glands, these being closely placed 
tubes vertically sunk into the mucous membrane. The epithelium lining the ducts is 
identical in appearance and nature with that of the free surface. Amongst the epithelium 
of both the surface and the gland ducts is a reticulum of connective-tissue cells and their 
processes (Watney), losing themselves in the cement substance between the epithelial 
cells. Watney showed that the epithelial cells, both of the free surface and of the 
ducts, undergo division ; this is indicated by the presence of smaller or larger epithelial 
buds, being groups of broad, clear epithelial cells. Underneath the epithelium is a base- 
ment membrane, which consists of nucleated flattened transparent endotheloid cells 
(Watney). 

The inner greater section of the mucous membrane belongs to the mucosa ; this 
contains in a scanty connective tissue, chiefly composed of thin fibre bundles, numerous 
flattened endotheloid cells (Watney), a few lymph corpuscles, and gland tubes, the 
gastric glands, placed closely and vertically to the surface. Owing to the close posi- 
tion of the gland-ducts, opening on the surface, the mucosa of this latter appears 



204 ATLAS OF HISTOLOGY. 

reduced to narrower or broader foldlike or villous projections. The glands of the 
pyloric end of the stomach, viz. the pyloric glands, possess a different structure from 
those of the rest of the stomach, the peptic glands. The latter are arranged in groups 
of four, five, and more. The amount of tissue of the mucosa separating these groups 
varies in different depths of the mucosa ; it is much greater near the surface, that is 
between the ducts, than in the depth. 

a) The Peptic Glands. — Into each of the above minute ducts, lined with the 
columnar mucus-secreting epithelium, open two or three tubes, the gland tubes proper. 
These are straight or slightly wavy, they are generally more or less curved like a 
hook at their blind extremity, that is, near the muscularis mucosae. The duct amounts 
to about a third or a sixth of the whole length of the tube ; near the cardia, the 
tubes being shorter, this relation is altered in favour of the ducts. 

The first section of the gland tube, amounting to about the third or fourth part of 
the whole tube, is the neck, the rest the body. The neck is much thinner than the body, 
and this latter increases in breadth towards the blind extremity, the fundus of the tube. 
At the point where the neck opens into the duct, the broad lumen of this latter 
becomes suddenly narrower and extends into the former as a very fine canal. The 
epithelium of the neck is a continuation of that of the duct ; its cells are, however, very 
much shorter, their substance is more opaque, and their nucleus small and oval. Out- 
side this epithelium lining the canal of the neck but inside the membrana propria of 
the gland tube we meet with other cells ; they are more or less angular, oval, or 
spherical cells slightly compressed in vertical diameter, of an opaque or 'granular' 
aspect, and containing a clear oval or spherical compressed nucleus ; they often bulge 
out the membrana propria, hence the outline of the tube becomes very irregular. 
These cells, which were formerly always described as the 'peptic cells,' were shown by 
Rollett and Heidenhain, who first recognised their true relation, to be always situated 
outside the epithelium lining the canal of the gland tube. Heidenhain called them 
parietal cells (Rollett's delomorphous cells), in contradistinction to the chief cells (Rollett* s 
adelomorphous cells), that immediately line the canal. They do not form a continuous 
layer but are isolated. In the neck they are tolerably near one another. 

The body of the gland tube also possesses only a fine canal lined by columnar cells 
or chief cells, these being a direct continuation of the chief cells of the neck, but much 
longer, more columnar, and more transparent than the former. They increase in length 
in proportion as the gland tube increases in breadth from the neck towards the fundus. 
The substance of these chief cells is a delicate reticulum with a small amount of a 
hyaline interstitial substance in its meshes (Klein). The nucleus is spherical or slightly 
oval, and situated in the outer third of the cell, it contains also an intranuclear network, 



STRUCTURE OF PEPTIC GLANDS. 205 

and stains readily in dyes. During digestion the chief cells of the body of the gland 
are thicker, hence the whole tube is slightly broader (Heidenhain) ; in this state the 
network forming the substance of the chief cells is more open, its meshes bein* larger 
The parietal cells are fewer than in the neck, but of the same position and structure ; 
their substance is opaque and the nucleus clear ; their number decreases towards the 
fundus (Rollett, Heidenhain). 

Owing to the different nature of the chief cells in the neck and the body of the 
gland, and to the difference in the number of parietal cells in the two sections, it is 
always possible to recognise, in a horizontal section through the gastric mucous mem- 
brane, the peptic glands being then cut transversely, whether a particular tube is cut 
across the neck or the body. More than this, owing to the difference in breadth of the 
body of the tube at the fundus, and further away from it, and owing to the parietal 
cells diminishing in numbers towards the fundus, it is possible to recognise whether a 
particular transverse section of a tube corresponds to the fundus or to another part of 
the gland. 

Approaching the pyloric end, the peptic glands alter slightly, inasmuch as the duct 
becomes longer and the tube relatively shorter ; the glands in some instances become 
branched at their fundus. Between the pylorus, containing the pyloric glands, to be 
described presently, and the rest of the stomach, there is, in carnivorous animals 
(dog), a zone (intermediary zone, Ebstein), in which the two kinds of glands, viz. the 
peptic glands and pyloric glands, not only intermix, but the first change into the latter 
(Klein, Bentkowski). This change consists in the following: (a) the ducts become 
very much longer : twice and three times as long as in other parts of the stomach ; the 
rest of the gland is accordingly shortened in proportion ; (/3) the neck of the gland 
becomes shorter ; (y) the body of the gland becomes branched, while the diameter of its 
lumen is very much enlarged; (S) the parietal cells diminish gradually in number, 
first in the body, then also in the neck of the gland. The chief cells retain their 
reticulated structure, both those of the neck and those of the rest of the gland. 

Careful observations have shown the existence of the two kinds of cells in the 
peptic glands of most mammals. Besides Rollett and Heidenhain, we owe these 
results to Friedinger, Jukes, Bentkowsky, Schafer and Williams, and others. Rabe 
does not find the two kinds of cells in the peptic glands of the horse. 

S) The Pyloric Glands. — From the description, just given, the nature of these 
glands is probably already clear. It is this : the duct is proportionately very long, it 
amounts to half or more of the whole length of the gland; two or three tubes open into 
the duct by a very short neck, which represents the narrowest part of the gland ; the 
body of the gland is branched into two or three tubes, which are wavy and convoluted ; 



i i 



2o6 ATLAS OF HISTOLOGY. 

the lumen of the neck, but especially that of the body of the gland, is much larger than 
in the corresponding parts of the peptic gland : the lumen in the body of the former 
glands being many times larger than that of the latter. 

The epithelium covering the surface of the mucosa and lining the ducts in the 
pyloric region is exactly the same as in the rest of the stomach. The epithelium lining 
the neck and body of these glands is a continuation of that of the duct ; but, as in the 
case of the peptic gland, so also here the cells are shorter and more opaque in the 
neck than in the body. In this latter the cells are fine, more or less transparent 
columnar cells : in no part are there parietal cells. Their substance is a beautiful 
reticulum, which during rest and exhaustion is closer and more elongated than during 
secretion ; in the latter state there is an appreciable amount of interstitial substance con- 
tained in its meshes. Hence the epithelial cells are shorter, more 'granular' and 
opaque during rest than during secretion ; in the former state the nucleus is spherical, 
during secretion it is compressed and close to the membrana propria (Ebstein, Klein). 

Ebstein regards the pyloric glands as simple peptic glands, but this is denied by 
several observers (v. Wittich and others) ; at any rate, they are not mucous glands, 
as formerly believed. 

Towards the duodenum the pyloric glands become larger, owing to the greater length 
of their tubes ; these are at the same time more branched. They pass without interrup- 
tion into the Brunner's glands, with which they are identical in structure. We shall 
return to these when describing the duodenum. 

The membrana propria of the glands of the stomach is of the same structure as that of other 
glands mentioned on former pages : viz. a network of flattened branched cells, from which come 
off filamentous and membranous processes that penetrate between the epithelial cells lining 
the gland tubes (Watney). The branched cells of the membrana propria of the peptic glands have 
been first seen by Henle ; Heidenhain described them more accurately. 

Outside the caecal extremity of the gland tubes is a thin layer of connective tissue, 
and then follows a muscular coat, the muscularis mucosae, which in some places consists 
of a single longitudinal layer, but in many places shows an inner circular and an outer 
longitudinal layer of unstriped muscle cells ; in some places there is an additional inner 
longitudinal or oblique layer. The thickness of the muscularis mucosae varies in differ- 
ent places ; as a rule it is thickest at the summits of the folds of the mucous membrane. 
Numerous bundles branch off from the muscularis mucosae and penetrate into the 
mucosa, where they ascend between the gland tubes ; near the surface some of them 
assume a horizontal course, others terminate at the basement membrane (Watney). 
Outside the muscularis mucosae is the submucous tissue, consisting of trabeculae of 
fibrous-connective tissue arranged as a loose meshwork. This tissue is here, as in 



STRUCTURE OF THE WALL OF THE STOMACH. w 

other parts, supporting the large blood-vessels and lymphatics, the nerve trunks and 
their ganglia. 

On the outer surface of the mucosa and the inner surface of the muscularis mucosa of cat's 
stomach is found a very characteristic elastic membrane (ZeissI), mentioned already in Chapter V. 

The mucous membrane composed of the preceding layers is fixed to a thick muscle 
coat, the external muscle coat, which in many places consists of an inner thicker circular 
and an outer thinner longitudinal stratum of unstriped muscle cells ; but masses of 
oblique bundles (fibrae oblique) are found on the inner surface of the circular stratum 
(Gillenskoeld). The outer boundary of the stomach is formed by the peritoneum, whose 
deeper bundles of connective tissue are connected with the perimysium of the longi- 
tudinal muscle stratum in the same way as those of the submucosa with the perimysium 
of the inner layer of the muscle coat. 

The mucous membrane of the first part of the alimentary canal.viz. mouth, palate, and pharynx, 
does not contain any muscularis mucosae, and the tissue of the mucosa passes therefore insensibly 
into that of the submucosa. Both these tissues, and especially the intermuscular connective 
tissue, contain fat-cells. 

In the second part, viz. the oesophagus, stomach, small and large intestine, the mucosa is 
separated from the submucosa by a muscularis mucosae, in the oesophagus, as mentioned above, 
it is a single longitudinal stratum, in the stomach it is composed of an inner circular and outer 
longitudinal stratum, and occasionally an additional inner longitudinal stratum. Fat-cells occur 
chiefly in the submucous tissue and in the subserous part of the peritoneal covering. 

In the mucous membrane of the mouth, palate, pharynx, and cesophagus, the secreting 
glands are situated in the submucous tissue; in the stomach, small and large intestine, they belong 
to the mucosa, except the Brunner's glands at the beginning of the duodenum, these are situated 
in the submucous tissue. 

The secreting glands of the alimentary canal, until the cardia is reached, are compound or 
branched tubular glands ; in the stomach, small and large intestine, they are single tubes with the 
exception of the pyloric glands and the Brunner's glands, both of which arc also compound tubular. 

The distribution of blood-vessels does not differ materially from that of the 
oesophagus, except in the mucosa. The arterial branches having penetrated through 
the muscularis mucosae ascend into the mucosa, where they dissolve themselves into 
capillaries, which form networks around the gland tubes, with more or less elongated 
meshes. Near the surface the network is very dense, and forms a special horizontal 
superficial layer underneath the epithelium. Out of this develop the venous branches. 

The lymphatics of the mucous membrane are very numerous, they form a deep 
plexus of larger vessels in the submucous tissue (Teichmann). Into this plexus lead 
lymphatics which belong to the mucosa: here they form, according to Teichmann and 
Loven, a network of vessels near the fundus of the gland tubes. According to Lovdn 
numerous lymphatics lead into that plexus ; these are larger than the former, and run 
a more or less longitudinal course between the gland tubes ; they anastomose with one 



I I 2 



2o8 ATLAS OF HISTOLOGY. 

another very freely, and extend nearly to the surface, where they form loops or 
terminate in saccular cecal extremities. In many places the lymphatics almost inva- 
ginate the gland tubes for a longer or shorter distance. In the mucosa, especially 
between the fundus of the peptic glands, are found occasionally smaller or larger masses 
of adenoid tissue. They form in some instances distinct lymph follicles, arranged either 
singly or in groups. At the point of union of the pyloric end of the stomach with the 
duodenum of man and other mammals occur numerous lymph follicles (Watney). 

The nerve trunks derived from both the pneumo-gastric and sympathetic include 

minute ganglia (Remak). The nerve branches, having entered the external muscle 

coat, form a plexus, extending in a horizontal direction between the longitudinal and 

circular stratum, the plexus of Auerbach. In this plexus are included spindle-shaped, 

angular or nodular ganglia. The ganglion cells are apolar, unipolar or multipolar. 

Nerve branches pass from the plexus of Auerbach into the submucous tissue, where 

they are again connected into a plexus, the plexus of Meissner ; this also includes minute 

ganglia, whose cells appear unipolar and bipolar. The structure of both these plexuses 

and their ganglia will be considered more minutely in connection with the small intestine. 

Rabe describes a rich plexus of nerve fibres surrounding the peptic glands of horse ; 

some of them terminate in peculiar spindle-shaped cells, each with two small nuclei. 



PLATE XXXI. 

Fig. I. From a vertical section through embryonal tooth of dog ; the tooth is still 
surrounded on all sides by the tooth sac. Magnifying power about 45. 

The preparation had been stained first in carmine and then in hematoxylin. 

a. Tooth papilla ; its cells and its blood-vessels are only indicated owing to the very 
low magnifying power. 

b. The layer of odontoblasts, the most peripheral stratum of the tissue of the 
papilla, is well shown. 

c. Dentin ; numerous fine lines pass through it, they agree with the outlines of the 
odontoblasts from which the dentinal matrix is derived, and correspond to the places for 
the future dentinal canals. There is a distinction between an inner thin layer of dentin 
next to the odontoblasts and an outer broader layer, the first is the most recently 
formed and not yet calcified. Next to this layer is the rudiment of enamel, marked by 
a thin layer of a substance stained deeply in hematoxylin. 

d. Inner membrane of the enamel cap, the columnar enamel cells are well shown. 

e. Middle membrane of the enamel cap, being a honey-combed structure. 















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■ 






STRUCTURE AND DEVELOPMENT OF TEETH. 209 

Outside this is the outer membrane or outer epithelium of the enamel cap, marked 
by a purple line. 

/ Tissue of the tooth sac with vessels; these latter do not extend further than 
the outer membrane of the enamel cap. 

Fig. II. From a similar embryonal tooth as in figure I., but of a stage when no 
middle membrane of the enamel cap is visible. Magnifying power about 400. 

a. Special layer of spindle-shaped and branched cells of the periphery of the tissue 
of the papilla penetrating with their long filamentous processes between the odontoblasts 
proper. These processes are much more numerous than represented here. 

b. The odontoblasts proper. 

c. Most recently formed layer of dentin, 
c x . Older dentin. 

c 2 . Enamel. 

d. Enamel cells ; between this layer and the following is a distinct membrane, 
omitted in the drawing. 

e. Outer epithelium of enamel organ ; its cells are separated from each other, probably 
in course of preparation. 

f. Tissue of tooth sac, a lamellated structure; the details of its structure have been 
omitted. 

Figs. III. and IV. Copied from Kolliker's ' Handbook/ 

In Fig. III. enamel prisms are seen in transverse section; in fig. IV. portions of 
enamel prisms seen lengthwise. 

Figs. V. and VI. Copied from Waldeyer (figs. 97 and 98) in Strieker's ' Handbook.' 
Fig. V. Frontal section through prsemolar tooth of cat. Magnifying power 15. 

1. Enamel, showing a radial striation due to the crossing of bundles of enamel 
prisms, and numbers of parallel stripes of Retzius. 

2. Dentin with the dentinal canals and Schreger's lines. 

The most peripheral dotted zone of the dentin corresponds to the interglobular 
substance. 

The central cavity corresponds to the pulp cavity. 

3. Cement ; in its transparent ground-substance are seen the large bone corpuscles. 

4. Periosteum of alveolus. 

5. Inframaxillary bone with the inframaxillary canal. 

Fig. VI. Part of dentin and cement from a transverse section of human canine 
tooth. Magnifying power 300. 

1. Cement with the large bone corpuscles. 

2. Interglobular substance. 



2IO 



ATLAS OF HISTOLOGY. 



3. Dentinal canals. 

Y\g. VII. Vertical section through part of enamel organ of a bicuspid tooth of 
puppy. Magnifying power about 300. 

a. Enamel cells; the upper part of the cells is here represented as of the same 
granular shade as the lower part containing the nucleus, in reality it is more transparent 
and homogeneous. 

b. Small epithelial cells, the deepest layer of which is composed of cells more or 
less columnar. The interstitial substance is represented as uniformly transparent, but 
this is in so far incorrect, as the cells are distinct 'prickle cells/ being connected by fine 
processes. 

c. The surrounding mucous membrane, projecting into the enamel organ as small 
papillae. 

A clump of small cells is seen in the neighbourhood of the epithelium. It is an 
outgrowth of the epithelium. 

Fig. VIII. From a section through submaxillary gland of a child. Magnifying 
power about 45 ; representing a lobule surrounded by fibrous-connective tissue. 

a. Chief duct, lined by columnar epithelium. 

b. Fibrous-connective tissue surrounding this and its lobule. 

c. Intralobular ducts. 

d. Its terminal parts. 

c. Alveoli, being tubes cut in different directions. 

Fig. IX. From a section through submaxillary gland of a child ; magnifying power 
about 350 ; showing part of a mucus-secreting alveolus and its several branches. 

a. Lumen of alveolus, the cells lining it are mucous cells. Outside these are 
polyhedral granular-looking cells each with a spherical nucleus. These cells form 
crescentic masses around the mucous cells. 

c. Alveoli cut in different directions, they are not mucus-secreting and correspond 
to true salivary gland substance. They are much smaller and have only a small lumen, 
the lining cells are columnar, each with a spherical nucleus. The cell substance appears 
granular because its intracellular network is exceedingly dense. 

PLATE XXXII. 

Fig. X. Part of a lobule of a serous gland of root of tongue of rabbit. Magnifying 
oower about 450. 

d. Duct. 

a. Alveolus or gland tube cut obliquely. 



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MUCOUS AND SALIVARY GLANDS, 211 

b. Gland tube cut longitudinally. 

The epithelial cells lining the alveoli are columnar, their substance is a dense net- 
work, much denser than here represented, and their nucleus is spherical. 

Fig. XL Part of a lobule of a mucous gland of the root of tongue of dog. Magni- 
fying power about 90. 

a. Gland tubes cut in different directions. 

d. Duct. 

Fig. XII. Part of a lobule of submaxillary gland of dog; showing (a) the alveoli 
cut in different directions ; each alveolus shows a relatively large lumen lined by trans- 
parent mucous cells, outside these the more opaque crescents of Gianuzzi. 

d. The intralobular ducts. 

The details in structure of the epithelium lining the duct and alveoli are not shown 
on account of the low magnifying power. 

Fig. XIII. From the same gland as represented in the preceding figure. Magnify- 
ing power about 400. 

a. Alveoli or gland tubes (branched) cut in different directions ; the lumen is very 
conspicuous ; the lining cells are mucous cells. Outside these are the crescents, groups 
of * granular ' polyhedral cells. 

d. Minute duct in transverse section ; its epithelium shows a very beautiful longi- 
tudinal striation. 

i. Intermediary part of duct. The epithelium is here made up of short columnar 
cells, each with a spherical nucleus. 

Fig. XIV. From a vertical section through the dorsal part of the tongue of a 
child. Magnifying power about 90. 

m. Connective tissue of mucosa. 

a. Small papilla filiformis. 

p. A papilla fungiformis. 

Both kinds of papillae are covered with thick stratified pavement epithelium, and 
both, especially the fungiform papilla, possess minute secondary papillae, extending from 
the connective-tissue matrix into the covering epithelium. 

Fig. XV. From a vertical section through dorsum of tongue of rabbit ; the blood- 
vessels had been injected with carmine and gelatin. Magnifying power about 100. 

m. Mucosa ; from it rise papillae filiformes, each with a single or double loop of 
capillary vessels. 

e. Thick stratified epithelium, covering the papilla?. 

/. The summit of the papillae ; the epithelium on them (summits), as well as on the 
surface between them — //—is transformed into a homogeneous horny stratum. 



ATLAS OF HISTOLOGY. 

Fiff. XVI. The duct and adjoining part of the mucous gland of fig. XI., but more 
highly magnified, about 450. 

d. Duct lined by a single layer of transparent polyhedral cells ; these pass into the 
mucous cells— g— of the infundibulum, but sooner on one side than on the other. 

The membrana propria with small flattened nuclei is well seen. 

Fig. XVII. From a section through true salivary gland structure of human sub- 
maxillary gland. Magnifying power about 350. 

a. Alveoli cut in different directions. 

b. Minute intralobular duct cut transversely ; its striated epithelium is well shown ; 
it is surrounded by fibrous-connective tissue. 

d. Similar duct cut longitudinally. 

PLATE XXXIII. 

Fig. XVIII. From a vertical section through the papilla foliata of rabbit. Magni- 
fying power about 90. 

f. Folds in transverse section, covered with stratified pavement epithelium ; at the 
basis of each fold are seen the taste goblets. 

g. Furrows between the folds ; into them open : 

d. The ducts of the serous glands. 

/. Lymphatic vessel in the centre of the folds. 

Fig. XIX. Three taste goblets more highly magnified, about 300. 

e. Epithelium around the taste goblets. 

g. Basis of the goblets next to the mucosa. 

//. Openings of the goblets with fine hairs. 

The distinction of the cells of the goblet in taste cells and tegmental cells is not 
shown here. 

Fig. XX. From a vertical section through a papilla circumvallata of a child. 
Magnifying power about 50. 

a. Fold of mucous membrane surrounding the papilla itself. 
/. The fungiform papilla, showing minute secondary papillae. 

Of the stratified epithelium only the nuclei of the cells are shown. 
At the basis of the papilla are seen the taste goblets. 
s. Serous gland ; its duct opens at the base of the papilla. 

7)i, A small section of a lobule of mucous gland between the lobules of serous 
gland. 

b. The vascular mucosa ; the holes are capillary vessels cut in different directions* 





















xxvin. 



XXV 




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5 







STRUCTURE OF GLANDS OF STOMACH. 213 

Fig. XXL From a vertical section through the pyloric end of the stomach of dog. 
Magnifying power about 150. 

s. Folds of mucosa covered with columnar epithelium. 

d. The glandular ducts lined with the same epithelium. 

?i. Region of the neck of the gland. 

m. Body of the gland tubes cut in different directions. 

mm, Muscularis mucosae, here composed of three layers. 

The tissue of the mucosa is here represented much denser than in reality. 

Figs. XXII. and XXIII. each represent a portion of a tube of pyloric gland, the 
former after prolonged secretion, the latter in ordinary secretion. Magnifying power 
about 500. 

In Fig. XXII. the intracellular network is much closer and the cell appears, there- 
fore, more ' granular,' the nucleus is spherical. 

a. The epithelial cells as seen from the surface. 

b. The same as seen sideways. 

In Fig. XXIII. the cells are more elongated, the meshes of the intracellular net- 
work wider, and the nucleus flattened. 

Fig. XXIV. Gland tubes of a mucous gland of oesophagus of dog. Magnifying 
power about 400. 

/. One gland tube cut transversely. 

/. Another as seen in longitudinal section. 

The epithelial cells lining the lumen arc mucous cells. The 'crescents/ com- 
posed of nucleated opaque cells, are seen in two places. 

Fig. XXV. From a vertical section through the mucous membrane of fundus of 
stomach (stained in aniline blue). Magnifying power about 50. 

d. Ducts of peptic glands, each taking up two thin gland tubes. 
The epithelium of the surface is of the same nature as in fig. XXI. 
;/.- Region of the neck of peptic gland. 

m. Body of the gland tube. 

The minute lumen of the gland tube is lined with columnar ' chief cells,' outside 
these are the deeply stained parietal cells. 

mm. Muscularis mucosae, composed here of two layers. 

s. Submucous tissue with a lar°-e vessel; between the fundus of the peptic glands 
and the muscularis mucosae is a small amount of connective tissue. 

Fig. XXVI. From a vertical section through the mucous membrane of esophagus 
of dog. Magnifying power about 50. 

e. Stratified pavement epithelium. 

K K 



2I4 ATLAS OF HISTOLOGY. 



m. 



i. Connective tissue mucosa, possessed of numerous minute papillae. 
mm. Muscularis mucosas, a single layer of longitudinal bundles of unstriped muscle 

cells. 

Outside this is the submucous tissue containing mucous gland tubes g, cut in 

different directions ; the wide infundibula of these pass into the ducts. 

d. Ducts which after penetrating through the mucosa open with a narrow funnel- 
shaped mouth on the free surface. 

Fig. XXVII. From a horizontal section through the mucosa of fundus of stomach 
of dog ; the section had been stained in aniline blue Magnifying power about 400. 

The peptic glands are cut transversely, they are arranged in groups separated 
by connective tissue including numerous unstriped muscle cells. 

c. Chief cells lining the small lumen of the gland. 
/. Parietal cells. 

Owing to the relatively great number of the latter, this section corresponds to a 
part nearer to the neck than to the fundus of the gland tubes. 

Fig. XXVIII. From a similar preparation to that represented in fig. XXV., but 
under a higher magnifying power : about 350. 

d. Duct ; the epithelium is the same on the free surface as in the duct, but the 
cells become shorter towards the neck. 

?i. Neck of the gland tubes, the chief cells lining the lumen are short columnar 
cells directly continuous with those lining the duct ; the parietal cells are here very 
numerous. 

In the body of the gland the chief cells are longer and more transparent than in the 
neck, and the parietal cells are less numerous. 

b. Fundus of gland tubes, its csecal extremity is slightly curved. 

Fig. XXIX. From a similar preparation as the preceding figure, representing the 
fundus of a gland tube under a magnifying power of about 450. 

c. Chief cells ; their substance is a distinct reticulum. 

/. Parietal cells ; the cell-substance is here a much denser reticulum. The nucleus 
of the parietal cells is always more transparent than that of the chief cells. 



2*5 



CHAPTER XXVI. 

THE SMALL AND LARGE INTESTINE. 

The wall of the small and large intestine consists, like that of the stomach, of the 
mucous membrane and the external muscle coat. The former is composed of; (i) the 
epithelium covering the free or internal surface; (2) the mucosa, which in the small 
intestine projects above the general surface as the villi ; in both the small and large 
intestine the mucosa contains simple vertical gland tubes with blind extremities in the 
depth and openings on the free surface, the crypts of Lieberkiihn ; (3) the muscularis 
mucosae ; and (4) the submucosa. The latter or external muscle coat includes : (a) an 
inner or circular layer of unstriped muscle cells ; (6) a middle or nervous layer, being 
a dense plexus of nerve branches and ganglia, the plexus mycntericus of Auerbach ; 
(c) an outer or longitudinal layer of unstriped muscle cells ; and (d) the peritoneum or 
serous covering. 

The connective tissue of the submucosa is united with the connective tissue separating 
the muscle bundles of the muscle coat next to it, and the same relation exists between 
the connective tissue of the serous covering and that of the longitudinal muscle layer. 

A. The Small Intestine. 

1) The epithelium. This is a single layer of beautiful columnar epithelial cells. The 
nature of the longitudinal striation of the cell substance, and the structure of the nucleus, 
the change the cells undergo during mucous secretion, and the nature of the striation of 
the free or basilar border, have been fully described and illustrated in Chapter II. It 
remains here to be added, that into the hyaline interstitial cement substance between the 
individual epithelial cells project filamentous or membranous structures, sometimes with 
nuclei, a sort of reticulum, continued from the tissue of the mucosa underneath. This 
relation has been referred to on a former occasion (Chapter XXII.). Lymph corpuscles 
are also occasionally met with between the epithelial cells (Watney). Where lymph 
follicles (see below) extend to the free surface, the epithelium of the surface becomes 
invaded both by the adenoid reticulum and the lymph corpuscles of the former ; under 
these circumstances the epithelial cells become altered, being greatly reduced in size, 
and changed into small irregularly shaped corpuscles in which the nucleus forms the 
chief part. 

L L 



2l6 ATLAS OF HISTOLOGY. 

In Chapter XXII. it has been mentioned that absorption by the epithelium in 
general takes place through the interstitial cement substance, whence the fluid or formed 
matter passes into the lymph-canalicular system of the tissue underneath, and from there 
enters the lymphatic vessels. The same holds good for the epithelium covering the 
villi of the small intestine with reference to the absorption of chyle : for the chyle 
globules travel, not through the substance of the epithelial cells themselves, but through 
the interstitial substance, and hence through the reticulum of the matrix of the villus, 
and finally into the chyle vessels. 

These statements arc based on observations of Dr. Watney, made under my direction. Dr. 
Watney's paper is published in the 'Philosophical Transactions/ 1876.— E. K. 

According to a generally received doctrine, the chyle globules are absorbed by the 
epithelial cells themselves, whence they pass into the tissue of the villus, and hence into 
the chyle vessel or vessels situated in the centre of the villus. This doctrine assumes that 
the substance of the epithelial cells becomes filled with the chyle globules, and further 
that it (the cell substance) is in direct continuity with the tissue underneath ; and, indeed, 
the literature on this subject is rich in assertions maintaining these two points, although 
there are equally numerous observers who deny them both. As mentioned above, the 
substance of the epithelial cells is concerned in the mucous secretion, not in absorption, 
which is performed by the interstitial substance, and this latter (interstitial substance) and 
not the former (epithelial cells) is connected with the tissue underneath. 

Amongst those who in more recent times asserted the absorption of chyle globules 
by the epithelial cells themselves and the passage from here into the tissue underneath 
may be cited Thanhoffer, who asserts that the chyle globules are taken up by the epi- 
thelial cells (of frogs small intestine) in virtue of active movement, dependent solely 
on the nervous system. This observer says the epithelial cells push out from their free 
surface minute processes, on and between which the chyle globules are caught, and then 
withdrawing the former also the latter are brought into the interior of the cell. 
By a repetition of this process the cells become gradually filled with chyle granules. 
In an equally splendid manner the cells are said to discharge the chyle globules into 
the tissue underneath, for each epithelial cell is possessed of two processes : one is in 
connection with the part of the tissue of the villus through which the chyle globules 
have to travel, and the other with a nerve fibril ; and thus the control by the nervous 
system of the whole proceeding finds a ready explanation. As regards mammalian 
animals Thanhoffer's view is,no doubt, erroneous. With reference to the special influence of 
the nervous system on the absorption of chyle, this is an assumption which for its support 
requires more evidence by facts than is at present available ; but this much must be said, 
that the whole process can be easily explained on the same simple principles as ab- 



CHYLE VESSELS OF VILLI. 2l? 

sorption in general (see Chapter XII.) ; viz. owing to the centripetal direction of the 
current in the lymphatic vessels, there is an . priori tendency of matter to pass from 
outs.de the lymphatic into the interior of this latter, and as both the wall of the 
lymphatic and the tissue surrounding it are permeable for formed .natter, this latter will 
find its way into the lymphatic. 

2) Underneath the epithelium is a basement membrane, which is composed of a 
s.ngle layer of flattened transparent endothelial plates, each with an oval nucleus, sub, 
epithelial endothelium (Debove, Watney). 

The tissue of the mucosa is similar to adenoid tissue, viz. a reticulum of fibrils and 
membranes, to which are applied from place to place transparent endotheloid plates 
each with an oval, clear nucleus ; in the meshes of the reticulum arc lymph corpuscles 
A few coarsely granular large plasma cells may be occasionally seen amongst them 
Each v.llus .s a projection of the mucosa. Villi vary in the intestines of different animals 
and in different parts of the same intestine. This difference consists in their length 
and shape : in some cases they are much flattened, leaf-like (hedgehog) ; in others less 
flattened (man, dog, cat) ; in the majority of cases they are conical if short (mouse), 
cylindrical if long (cat, dog). 

The tissue of the villi is similar to, but not identical with, that of the rest of the mu- 
cosa. It possesses in the centre one or two relatively large chyle vessels ; these are in 
all respects identical with lymphatic capillaries, their wall being made up of a single layer 
of endothelial plates (v. Recklinghausen). They terminate with a blind extremity near 
but not quite at the summit of the villus. Along this chyle vessel or vessels run thin 
bundles of unstriped muscle cells (BrUcke). They extend from the base to near the 
summit of the villus ; in many places they may be traced from the tissue of the mucosa, 
in others this does not seem to be so. The individual cells are relatively long, like the 
muscle cells of the alimentary canal generally. 

In a transverse section through a villus the muscle bundles appear arranged around 
the chyle vessel, without, however, always forming a continuous layer (Basch). 

Thanhoffer mentions also circular muscle cells situated in a transverse direction on 
the surface of the villus immediately underneath the epithelium. 

On their way towards the summit the bundles of muscle cells become much 
attenuated by giving off laterally individual muscle cells that terminate at the basement 
membrane of the sides of the villus. Those muscle cells that reach the summit 
terminate also on the basement membrane (Watney). 

I he matrix of the villus consists of a homogeneous delicate reticulum, in the 
meshes of which lie flattened cells of various sizes, each with an oval clear nucleus, and 
arranged like an endothelium (Watney). There are all gradations between these 



L L 2 



21 g ATLAS OF HISTOLOGY. 

endothelial cells and the lymph corpuscles as present in the mucosa. In some places 
there may be noticed a branched cell with a small nucleus included in the reticulum. 

The reticulum just mentioned represents at the same time the interstitial substance 
for all other elements in the villus ; viz. muscle cells, blood-vessels, and endothelium of 
the chyle vessels (Watney). It extends through the basement membrane (as the inter- 
stitial substance between its individual endothelial plates), and becomes identified with 
the interstitial cement substance between the epithelial cells covering the free surface of 
the villus. 

The paths for the chyle globules are, then, these : the interstitial substance of 
the epithelium, the interstitial substance of the basement membrane, further the 
reticulum forming the matrix of the villus, and finally the interstitial substance 
between the individual endothelial cells forming the wall of the chyle vessel. All 
these substances are soft, probably semifluid in the living state, and do not present any 
obstacle to the passage of formed matter. 

Since there exists the same anatomical continuity between the reticulum on the one 
hand and the interstitial substance of the endothelial cells forming the wall of a venous 
capillary on the other (Watney), there is no reason why the chyle globules or other 
matter, to be absorbed, should not pass with the same facility into the venous rootlets 
as into the lymphatics, since the current is in both centripetal. 

At the base of the villi open the crypts of Lieberkuhn. They are vertically 
arranged, and so closely placed side by side that only a small amount of tissue of the 
mucosa is found separating them. The length of the crypts varies in different parts of 
the intestine, the longest being found in the duodenum, owing to the greater thickness 
of the mucosa in this latter place. The crypts are about as long as the mucosa is 
thick, that is their blind extremity is almost in contact with the muscularis mucosae. 

Each crypt consists of a membrana propria, which, being a continuation of the base- 
ment membrane, is in reality an endothelial membrane (Watney). In connection with 
this latter, probably with its interstitial substance, are filamentous and membranous struc- 
tures penetrating towards the lumen of the crypt ; they form a reticulum, including a 
nucleus in some places, and become identified with the interstitial substance separating the 
columnar epithelial cells lining the crypt. These epithelial cells are identical in structure 
and function with those covering the free surfaces of the villi, as has been described and 
figured in detail in Chapter II., except that they are somewhat shorter. 

3) The muscularis mucosa is in many parts composed of an inner thin circular 
and an outer equally delicate longitudinal layer of unstriped muscle cells, but in some 
parts of the small intestine only a single longitudinal layer can be detected. 

4) The sudmucosa is composed of trabecular of fibrous-connective tissue, forming 



SUBMUCOUS TISSUE OF SMALL INTESTINE. 8IQ 

a loose meshwork ; it is the carrier of the blood-vessels, nerves, lymphatic vessels 
and fat fssue. The structure and arrangement of the lymph follicles, which, as mentioned 
m a former chapter, occur as solitary or agminated glands, and in the latter instance pro- 
duce the Preyer's patches, have been fully described on page I59 . With their body and 
fundus they are situated in the submucous tissue ; with their summit they are pushed 
through the muscularis mucosae and reach the free surface of the mucosa, and are covered 
with columnar epithelium more or less altered by the ingrowth of the adenoid tissue 
In the mucosa the adenoid tissue of the lymph follicles merges into the tissue of the 



former. 



The submucous tissue of the first part of the duodenum contains the glands of 
Brunner. These are closely placed, and form a special layer in the submucosa next to 
the muscularis mucosa. Each gland is a branched and convoluted tube (Schlemmer 
Schwalbe, He.denhain), with large lumen lined by columnar cells of exactly the sami 
structure as those of the pyloric glands (Schwalbe, Watney and others). They undergo 
the same changes in their structure during rest and secretion as the cells of the pyloric 
glands (Hirt, Klein). The lumen of the gland tube is continued into minute capillary 
channels between the epithelial cells lining the lumen (Schwalbe, Klein). The duct 
emerges from the gland next to the muscularis mucosa,, passes through this and ascends 
in a vertical direction between the crypts of Lieberkuhn of the mucosa, and opens on 
the free surface of this latter. The duct is narrowest at its beginning-neck of the 
gland-and is lined by simple columnar epithelium. The difference between a gland of 
Brunner and one of the pyloric end of the stomach consists chiefly in the much greater 
length of the duct and in the greater length and number of the tubes belonging to one 
gland. 

The glands of Brunner are separated by thin trabecule of fibrous-connective 
tissue ; bundles of unstriped muscle cells, derived from the muscularis mucosa.-, pass 
between and outside them (Verson). 

Where the pyloric end of the stomach is in contact with the duodenum the pyloric 
glands can be directly traced into the Brunners glands (Cobelli, Watney), the tubes 
becoming larger, more numerous, and being gradually pushed from the mucosa into the 
submucous tissue. At the point of transition the muscularis mucosa is generally more 
or less interrupted. In the dog there is a zone of appreciable dimensions that does not 
possess any continuous muscularis mucosa?, and in this zone the transformation of the: 
pyloric glands into the glands of Brunner is very well shown. 

With regard to the external musck eoat there is little to be added to what has 
been already mentioned ; the circular layer is generally thicker than the longitudinal. 
The plexus myentericus of Auerbach, situated between the two muscle layers, is 



22Q ATLAS OF HISTOLOGY. 

composed ot finer and thicker flat bandlike nerve branches ; each of these is ensheathed 
in a delicate endothelial membrane, being a continuation of the perineurium of the nerve 
trunks entering the intestine, and is composed of a number of fine elementary nerve 
fibrils. A grouping of these into separate axis cylinders is nowhere distinguishable. 

The plexus contains many triangular or irregularly shaped placoid enlargements, 
in which groups of ganglion cells are embedded. These are either closely grouped 
together and separated only by a few fibrils, or they are arranged in clusters or nests, or 
form chains and rows. These latter may be seen extending specially from the placoid 
enlargements into the afferent or efferent branches. 

The ganglion cells vary very greatly in size, some being many times larger than 
others. The smallest consist of a nucleus surrounded by just a trace of cell substance ; 
the largest ones are like ordinary full-grown sympathetic ganglion cells, from which 
they do not differ in structure of their cell substance and nucleus. As regards the shape 
of the ganglion cells, they are spherical, elliptical, or branched (unipolar, bipolar, and 
multipolar) ; only the larger ones are possessed of a capsule and processes. 

From this plexus come off minute branches, which, having split into fine fibres, 
form secondary plexuses for the different strata of the circular and the longitudinal 
muscle coat. These represent the plexuses for the muscle bundles, and correspond 
therefore to the intermediary nerve plexuses of unstriped muscle tissue (see p. 131). 

From the plexus of Auerbach pass nerve branches through the circular muscle layer 
into the submucous tissue, where they are connected into the plexus of Meissner. The 
branches of this are more cylindrical, and at the points of anastomosis they form nodular 
or spindle-shaped enlargements. Here are groups or chains of ganglion cells much 
more uniform in size and appearance than in the plexus of Auerbach ; many of the 
ganglion cells are enclosed in a capsule, and are unipolar, bipolar, and multipolar. 

From the plexus of Meissner originate other minute secondary plexuses of nerve 
fibres, most of which are destined for the bundles of the muscularis mucosae, but there 
are minute networks belonging to the connective tissue and blood-vessels of the sub- 
mucosa. 

The blood-vessels are arranged in various systems according to the very different 
tissues forming the wall of the small intestine. The first system is that of the peritoneal 
covering ; then the external muscle coat contains the second system ; the fat tissue when 
that occurs in larger masses in the submucosa ; the lymph follicles and the Brunner's 
glands (in the duodenum) contain each their own system ; the muscularis mucosae 
has again its own vessels, the mucosa including the villi possesses the final and 
most important system. In all these cases the afferent arteries or efferent veins are 
branches of the respective trunks, entering the intestine at the mesenteric margin. 



BLOOD-VESSELS OF SMALL INTESTINE. 
The arterial and venous trunks found in the submucosa give off or take up 
respectively the vessels for all the above systems present between the epithelium of the 
inner surface and the external muscle coat. 

The distribution of the capillaries in the peritoneal covering is the same as in the 
mesentery, viz. uniform networks with rather large meshes ; those of the external muscle 
coat and the muscularis mucosa? are arranged as in other unstriped muscle tissue, viz. 
networks with elongated meshes. The capillary network of the fat tissue is the same 
as in fat tissue of other parts (see Chapter VI.). 

In the solitary and agminated lymph follicles the capillaries form a network with 
elongated meshes and radiating towards the centre, where they generally form loops. 
Around the individual follicles minute veins are found arranged as a special network. 

The arterioles passing through the muscularis mucosa: into the mucosa give off 
numerous capillaries, forming a network around the crypts of Lieberkiihn ; their meshes 
are elongated and vertical to the surface ; the arteriole passing j nto the villus ascends 
generally to near the apex, except in man, where it does not as a rule pass beyond the 
lower half (Heller). It dissolves itself into a dense network of capillaries, spreading 
over the apex and base of the villus ; in the former the network is much denser than in 
the latter. 

The capillaries of the villus are always situated in the periphery next to the 
epithelium. The network of capillaries of the villus forms a continuity with that of the 
rest of the mucosa (Toldt). 

There are generally one or two veins developed from the capillaries of the villus. 
According to Heller, the vein generally commences near the apex of the villus in man 
and rabbit, while in dog, cat, pig and hedgehog it originates near the base. 
The lymphatics of the small intestine are very numerous. They are : 
a) The lymphatics of the villi. As has been mentioned above, each villus has a 
central single chyle vessel, or two such vessels, anastomosing with one another. They 
correspond to large lymphatic capillaries, beginning with a blind extremity near the apex of 
the villus; the reticulum of the surrounding tissue is connected with the interstitial sub- 
stance of the endothelial wall and represents the rootlets for the chyle vessel. At the basis 
of the villus the chyle vessel is generally much narrower and anastomoses with the network 
of lymphatic capillaries and sinuses between the Lieberkuhn's crypts (Frey and others). 
Absorption by the chyle vessels is in a great measure supported by the peculiar 
relation existing between the blood-vessels of the villus and its chyle vessel, for during 
digestion the former are in a state of great turgescence, and owing to their peripheral 
disposition will necessarily keep the villus erect : the central chyle vessel is hereby, of 
course, kept distended. 



222 ATLAS OF HISTOLOGY. 

b) The lymphatics of the rest oi the mucosa appear as a network of finer and 
broader capillaries and sinuses ; these latter surround in many places the crypts of 
Lieberkuhn to a greater or smaller extent. Just below the fundus of the crypts of 
Lieberkuhn this network of lymphatics is denser and more easily visible. 

c) These lymphatics send their efferent branches into the submucosa, where they join 
larger lymphatic tubes with valves : they are connected into a network. When there 
are lymph follicles, they (tubes) take up the lymph sinuses surrounding a greater or 
smaller section of the surface of the basis of the follicles (His, Frey, and others), (see 

p. 164). 

d) While the efferent trunks of the submucous lymphatics penetrate through the 
external muscle coat, in order to reach the mesenteric margin, they take up the lymphatic 
system of the former. This system is a network of lymph capillaries situated between the 
circular and longitudinal layer ; they take up straight channels and clefts between bundles 
of unstriped muscle fibres, chiefly of the circular layer. These channels are lined with 
endothelium, possess no valves, and their arrangement is, of course, parallel with the 
direction of the bundles. 

c) The peritoneal covering possesses its own network of lymphatics, the efferent 
trunks of which join the large lymphatics in the mesenteric margin. The subserous 
lymphatics take up many lymphatic channels and clefts of the adjoining longitudinal 
muscle layer. 

The blood-vessels of the muscle coat are occasionally seen invaginated in a peri- 
vascular lymphatic, representing one of the above-named lymph channels or clefts 
between muscle bundles. 

B. The Large Intestine. 

The structure of the large intestine is in many respects identical with that of the 
small intestine, only slight differences existing between the two. 

The epithelium covering the inner surface, the mucosa and the crypts of Lieberkuhn, 
possess the same nature in both organs ; there are no villi, but in some instances, as in 
the colon of rabbit, the mucosa is raised in the form of minute permanent papillae, but 
these are altogether different from villi of the small intestine, for they (papillae) contain 
crypts of Lieberkuhn like other parts of the mucosa. Of interest are the bundles of 
unstriped muscle cells, ascending into these papillae and terminating at the basement 
membrane (Watney). 

The muscularis mucosae consists in most places of an inner circular and an outer 
longitudinal layer. Minute bundles may be occasionally seen branching off from the 
inner layer and ascending between the crypts of Lieberkuhn. 



STRUCTURE OF LARGE INTESTINE. 

The submucosa contains, as a rule, m0 re fat-cell tissue than the small intestine, but 
otherw.se shows the same structure. The l ymph f ollicles occur ^ ^ 
follicles ; they are much larger than in the small intestine, and are either pushed thro,,,, 
the muscular, mucosae with their summit, or, what is in some large intestines (pig) 
more commonly the case, the mucosa with its crypts of Lieberkuhn is. to a greater or 
smaller extent, drawn down into the lymph follicle through a discontinuity of the muscu 
lans mucosa,. In these instances there is, consequently, to be found a pit lined with crypts 
of L.eberkuhn, and leading into the depth to the lymph follicle. In man and carniverous 
animals a relation resembling this is occasionally met with. The abundance of lymph 
follicles and their arrangement (as Peyers patches) in the ccecum of rabbit have been 
described and figured on p. 169. 

The processus vermiformis of man contains numerous lymph follicles, closely placed 
and arranged like those of the Peyers patches of the small intestine. 

The external muscle coat of the caecum and colon differs in so far from that of the 
small intestine that in some parts the circular and longitudinal layer is very thin or alto 
gether wanting; in the septa of the well-known sacculi the circular bundles form groups, 
and similarly the so-called ligaments represent accumulations of longitudinal bundles. 
In the rectum, whose mucosa is of conspicuous thickness, the external muscle coat is 
well developed, the circular layer being of great thickness. 

The nervous apparatus is the same as in the small intestine, except that the sub 
mucous plexus of Meissner contains larger ganglia than that of the small intestine, and 
that the ganglion cells appear smaller in the former than in the latter. 

The plexus of Auerbach of the large is more developed than that of the small 
intestine, the nerve branches being more numerous, the plexus denser, and the ganglionic 
enlargements greater. In the toad I have observed large isolated multipolar ganglion 
cells situated in the meshes of the general plexus; some of their processes are connected 
with the branches of this, while others pass as fine fibrils directly amongst the muscle 
bundles, forming on these a more or less distinct transparent plate-like expansion. 

The distribution of blood-vessels and lymphatics is very similar to that of the small 
intestine. 



M M 



224 ATLAS OF HISTOLOGY. 



CHAPTER XXVII. 

THE PANCREAS. 

The structure of the pancreas differs to a considerable extent from that of the salivary 
glands. The two are, however, similar as regards the framework, the blood-vessels and 
lymphatics. A thin capsule of fibrous tissue gives off lamellae of the same tissue ; these 
penetrate as septa between the lobes and lobules into which the gland substance is 
divided. The amount of this connective tissue varies in different animals ; in man it is 
greatest and therefore the arrangement of the gland into lobes and lobules can be easily 
followed. From the interlobular connective tissue proceed very delicate bundles of 
fibrous tissue, but especially the flattened branched connective-tissue corpuscles ; these 
are continued into the interior, where they may be traced, in company with the capillary 
blood-vessels, between the gland alveoli. 

The interlobar and interlobular connective tissue gives also support to the larger 
branches of the arteries and veins, and it contains nerve branches and large lymphatics with 
valves. These latter take up lymphatic clefts and sinuses lined with endothelium and 
situated between tlie lamellae of connective tissue passing in between sections of a lobule. 
In man these lymphatic clefts are easily demonstrated and also the sinuses which sur- 
round parts of the circumference of the alveoli. 

As regards the distribution of blood-vessels the same relations prevail as in the 
salivary and other glands, viz. the arterioles dissolve themselves into a uniform net- 
work of capillaries closely surrounding the alveoli. 

The gland lisstie consists of the large or lobar ducts, which take up the small or 
intralobular ducts ; these are much branched and take up longer or shorter branched 
thin canals which correspond to the intermediary parts of the ducts ; these lead directly 
into the alveoli. 

The lobar ducts are tubes with large lumen, their wall is a membrana propria 
lined with short columnar epithelial cells, each with an oval nucleus near the membrana 
propria. The cells are shorter than in the ducts of the salivary glands, and their sub- 
stance is very finely and longitudinally striated. Outside is a smaller or larger amount 
of fibrous-connective tissue ; the pancreatic duct and its larger branches possess in their 
wall unstriped muscle cells. 

The intralobular ducts are similar to the former, except that they are much smaller : 



STRUCTURE OF PANCREAS. 
their epithelium being shorter and the lumen Smaller, and the fibrous tissue around Z 
much ess m amount. The substance of the epithelial cells is transparent, and does not 
show, he that of the cells hnmg the intralobular ducts of the salivary glands, thick 
rodhke fibres. The nucleus of the cells is more or less spherical 

The intermediary parts are branched canals of various lengths wit., a small, but 
chstmct lumen; each conststs of a membrana propria, a continuation of the same men, 
brane of the mtralobular duct, lined with a single layer of flattened clear cells more or 
less elongated, and each with a flattened oval nucleus (Langerhans, Teraszkievicz) 
I he intranuclear network is very well seen. 

These cells are continuous with the lining cells of the intralobular ducts 
The length of the intermediary canals varies in different parts: while in some 
lobules they and their branches may be traced for a considerable distance, in others they 
are extremely short, the branches of the intralobular ducts appearing to pass almost 
.mmed.ately into the alveoli. The intermediary tubes in the pancreas of rabbit are very 
long (Langerhans). 

The alveoli are branched tubes, very wavy and much convoluted. They are 
hmited by a membrana propria of the same structure as that of the salivary glands (see 
the chapter on salivary glands), lined with a single layer of beautiful columnar cells • 
these are either cylindrical or blunt conical with their narrow end in the centre of the 
alveolus. Their substance shows a marked distinction into an inner and outer part 
(Langerhans, Heidenhain); the outer part (that is the one next the membrana propria) 
is homogeneous in aspect and stains better with dyes; the inner appears more, granular 
and does not stain readily (Heidenhain). The nucleus is spherical and is placed in the 
outer part where this is in contact with the inner part. These two zones of the epithelial 
cells differ in structure in this manner : while the outer zone is composed of very fine 
longitudinal fibrils (Pfltiger, Heidenhain), the inner, viz. the one that appears coarsely 
granular and is described as such by Langerhans and Heidenhain, is in reality a network 
of thick short rods (Klein). When viewing this part of the cell substance in an oblique 
manner the rods are very clearly seen; viewed from the top they appear as closely placed 
coarse granules of uniform size. The nucleus contains a distinct network. 

According to Heidenhain the cells alter their appearance and size in different 
stages of digestion in this way: in the first stage of digestion the cells as a whole become 
smaller owing to a diminution (exhaustion) of the inner or granular zone, but the- outer 
zone appears at the same time slightly larger ; in the second stage a regeneration takes 
place of the granular inner zone at the expense of the homogeneous outer one ; this 
latter considerably decreases, but the cell as a whole increases greatly in size 

Kuhne and Lea, observing the pancreas of rabbit during life, noticed that during 



M M 2 



226 ATLAS OF HISTOLOGY. 

hunger the outline of the gland tubes is quite smooth, while during digestion it be- 
comes irregular, being notched-in, corresponding to the outlines of the lining epithelial 
cells. This condition can be easily confirmed in hardened specimens. They also 
noticed that the striation of the outer zone of the cells is more distinct during 
digestion. 

The cells are separated from one another by a thin layer of a homogeneous interstitial 
substance, which corresponds to the ultimate or capillary secreting canals (Latchenberger 
and others ; see the reference to the various assertions as regards the pancreas and 
salivary glands in Chapter XXIII.). 

The centre of the alveoli is occupied by the same interstitial substance, there being 
visible, as a rule, no distinct lumen or only a trace of such an one. In all parts of the 
gland tubes the place of the lumen is occupied by spindle-shaped or branched cells, each 
with an oval nucleus, the centroacinar cells of Langerhans. It is difficult to definitely 
ascertain whether these centroacinar cells are continuations of the cells of the inter- 
mediary parts of the ducts (Langerhans, Teraszkievicz) or not ; if the former be the 
case, the epithelial cells lining the alveoli would be altogether independent of those 
lining the intermediary part, and the latter would, then, be continuous with the alveoli 
only by means of the membrana propria and the centroacinar cells. 



227 



CHAPTER XXVIII. 

THE LIVER. 

The framework of the liver is composed of the capsule, the inter- and intralobular 
connective tissue. 

The capsule is fibrous-connective tissue, covered with endothelium on its free 
surface ; like that oi other serous membranes, it consists of trabecule of connective-tissue 
bundles crossing each other in various directions, and between them are the flattened 
branched connective-tissue corpuscles. In man the connective tissue of the capsule 
forms two distinct strata (Theile), an outer, containing in the matrix of fibrous-connective 
tissue networks of elastic fibrils, and an inner stratum, more lamellar in its structure 
and continuous with similar masses of connective tissue separating the lobules. 

The latter, viz. the interlobular tissue, or the tissue of the portal canals (Glisson's 
capsule), is also more or less lamellar, the bundles of the individual lamellae running in 
various directions ; between the lamellae are the flattened branched connective-tissue 
corpuscles in their respective interfascicular lymph spaces, and in very youne livers in 
addition a few migratory cells. 

The interlobular connective tissue forms the supporting tissue for the blood-vessels, 
lymphatics, nerves, and bile ducts. 

The arrangement of the interlobular tissue determines the size and shape of the 
lobules or acini. According to whether this tissue forms complete septa between the 
lobules or not, these latter appear well defined from one another (pig), or more or less 
confluent (man and many other mammals). In the former case the lobules are poly- 
gonal, more or less oblong or cubical, in the latter their outline is very irregular, 

The intralobular connective tissue is very delicate and scarce, it consists of: 

a) Flattened branched connective-tissue cells (Fleischel, Kupffer) situated between 
liver cells and blood capillaries. These corpuscles are continuous with each other in a 
network, and at the margin of the lobules also with those of the interlobular tissue. 

b) There is a small amount of fibrous-connective tissue around the intralobular or 
central vein ; this (connective tissue) is a continuation of the fibrous tissue surrounding 
or supporting the hepatic vein. 

c) Minute bundles of fibrous tissue extend between the interlobular connective 



228 ATLAS OF HISTOLOGY. 

tissue and the tissue surrounding the central vein of each lobule (Fleischel, Ewald 

and Kiihne). 

Asp, and especially Pcszke, mention also the existence of a network of fine fibrils, probably 
of the nature of elastic fibrils. 

The blood-vessels. The interlobular branches of the portal vein, at the margin of 
the lobules, give off the exceedingly numerous capillaries for the latter ; these are 
extending in a direction radiating towards the central vein into which they open. These 
radiating or longitudinal capillaries are connected by transverse or horizontal branches 
into a network. The transverse branches are in some livers more numerous (man, 
especially dog) than in others (rabbit) ; in the former instances the meshes of the 
capillary network are more uniform, in the latter they are oblong, of course in a radiating 
direction. 

The branches of the hepatic artery are interlobular and accompany the branches of 
the portal vein, which latter in some places are surrounded by them (arteries) as by a 
plexus; they anastomose with one another in many places, and finally give off capillaries 
for the connective tissue of the portal canals and all the structures embedded in it, 
especially the bile ducts (Kowalewsky). They lead into special veins (Ferrein), which 
accompany in couples (Beale) the arteries and join the interlobular branches of the portal 
vein. According to many observers the capillaries and veins derived from the hepatic 
artery join the capillaries of the lobules directly ; and according to Kowalewsky this takes 
place by the anastomosis of the blood capillaries of the bile ducts, or of the venous 
branches proceeding from them, with the capillaries of the lobules at the margin 
of the latter. But according to Cohnheim and Litten the number of capillaries, 
derived from the hepatic artery, and anastomosing with the capillaries of the lobules, is 
but a small one. 

The capsule of the liver possesses its own branches of the hepatic artery, viz. 
the rami capsulares : these dissolve themselves into a dense network of capillaries, 
possessing in some places a stellate arrangement. 

The gland substance proper is arranged as the tissue of the lobules or acini, and 
as the bile ducts. Each lobule consists of small polygonal epithelial cells, the liver 
cells, permeated by the above-named capillary blood-vessels. These two structures, viz. 
liver cells and capillary blood-vessels, represent the chief parts of the lobule ; the branched 
connective-tissue corpuscles and the very few fine bundles of fibrous tissue, especially 
around the central vein, form only a small addition. There is no membrana propria 
separating the liver cells from the capillary vessels. The liver cells in man and mammals 
are arranged neither as a network of ( cylinders ' or ' trabecular ' radiating towards the 
central vein and separated by the capillary vessels, nor as a compound tubular gland in 



ng 



STRUCTURE OF LIVER CELLS. 
the ordinary sense, but they form within each lobule one continuous mass of cells per- 
meated only by the capillary blood-vessels (Hering) ; owing to the peculiar arrangement 
of the latter a vertical section through the lobule shows a network of longer radiati 
and short transverse masses of liver cells. The latter are about of the same size through 
out the liver, but there are some, especially near the margin of the lobules, that are 
smaller than the rest. Their shape is polyhedral (in section pentagonal or hexagonal) 
or sometimes slightly elongated, their surface smooth and separated by a hyaline inter- 
stitial substance. Kolatschewsky isolated liver cells that were possessed of processes. 

The substance of the cells appears uniformly granular, but is in reality a beautiful 
honeycombed network (Kupffer, Klein). It is probable that during activity the meshes 
of the intracellular network are larger, and hence also the cell as a whole becomes enlarged. 
Each cell possesses one spherical or slightly oval nucleus; in the liver of rabbit it is 
common to find cells with two nuclei ; in some livers there are liver cells without any 
nucleus (Asp, Peszke). The nucleus is limited by a thin membrane, and includes an 
intranuclear network, in which occasionally one or two thickenings, nucleoli, are seen. 
The intranuclear network forms a continuity with the intracellular one ; the network of 
contiguous cells is likewise in connection with one another (Klein). 

Besides the liver cells and capillary blood-vessels there are in each lobule numerous 
minute cylindrical canals, the bile capillaries, which form a network closed in itself 
(Hering). These bile capillaries run between the contiguous liver cells, so that the 
meshes of their network are of the size and shape of the cells (Hering, Eberth, Kfllliker). 
The bile capillaries when viewed in section are found in the angle where three or more 
liver cells meet (Eberth, Peszke). They are never present between liver cells and ca- 
pillary blood-vessels (Hering, Peszke). Owing to the radiating arrangement of the 
whole mass of the liver cells, we meet in many places with bile capillaries extending for 
a considerable distance, in a similar, i.e. radiating, manner, and giving off short lateral 
branchlets ; this gives rise to the appearance, as it were, of long chief bile capillaries 
and short lateral secondary branchlets. 

Some observers assume a special delicate membrana propria forming the wall of the 
bile capillaries (MacGillavry, Chrzonszewski, Asp, Peszke, Davis and others), while 
Hering, Eberth, Kolliker and others deny the existence of a definite membrane, as that, 
for instance, forming the membrana propria of other gland ducts, and assume that the 
liver cells themselves form the immediate boundary of the bile capillaries. 

The bile ducts are situated in the interlobular connective tissue ; they are the 
efferent ducts : tubes with a relatively large lumen, a lining columnar epithelium 
and a limiting membrana propria with regularly disposed oblong nuclei in it, most pro- 
bably owing to its being an endothelial membrane. The largest ducts are surrounded 



ATLAS OF HISTOLOGY. 

by unstriped muscle cells (Heidenhain), The epithelium lining the small ducts is made 
up of short columnar cells, that of the large ducts is distinctly columnar. The bile ducts 
form a network amongst themselves (Beale). At the margin of the lobule the small 
ducts are much branched ; their branches are narrow tubes with a very small lumen, 
and arc lined with a single layer of small more or less flattened epithelial cells ; a 
distinct membrana propria forms the outer boundary. These so constructed tubes 
correspond to the intermediary portion of the ducts of other glands (see previous 

chapters). 

Now, the intermediary portion of the bile ducts joins the substance of the lobule 
in this manner: the lumen of the former passes directly into the network of bile capil- 
laries, while the flattened epithelium, changing of course suddenly its appearance and 
nature, forms a direct continuity with the mass of the liver cells. At the point of the 
union of these two the difference between the respective cells is sufficiently striking ; the 
cell-body and nucleus of the liver cells are much larger than the corresponding parts of 
the cells of the intermediary duct ; the nucleus of the latter forms the most conspicuous 
part of the cell, it stains deeply in dyes and is surrounded by very little cell substance ; 
the breadth of the whole intermediary tube is greatly inferior to the diameter of two 
liver cells. The membrana propria is not continued into the lobule on to the surface of 
the liver cells, as is maintained by Beale, Pfluger and others. 

The interlobular connective tissue, as well as the capsule of the liver, possesses net- 
works of lymphatics ; those of the latter, viz. the superficial lymphatics, form an exceed- 
ingly dense network of fine vessels, denser even than the blood capillaries of the branches 
of the hepatic artery (Hering). With this network communicates the network of the 
deep lymphatics, viz. those situated in the connective tissue of the portal canals ; the 
vessels of this system are fine and large vessels ; the latter have valves. Networks of 
these interlobular lymphatics surround the branches of the portal vein as well as those 
of the hepatic vein (Kolliker, v. Wittich), and also the branches of the hepatic duct (v. 
Wittich). According to Budge and Kowalewsky branches of the hepatic vein are com- 
pletely ensheathed in lymphatic vessels; a fact easily confirmed. The fine interlobular 
lymphatic vessels are, at the margin of the lobules, in communication with minute 
spaces extending between the liver cells and the capillary blood vessels (MacGillavry, 
Frey and others), and containing the branched connective-tissue corpuscles mentioned 
above. Under normal conditions these intralobular lymph spaces are very insignificant, 
but may become much distended and conspicuous under abnormal conditions through 
accumulation of fluid or formed matter. According to Kisselew and Chrzonszewsky 
small lymph follicles may be present in the interlobular connective tissue. 

The wall of the large branches of the hepatic duct consists of a mucous membrane 



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STRUCTURE OF GALL BLADDER, ; 3 < 

of loose connective tissue with numerous capillary blood-vessels and lined with a 
single layer of beautiful columnar epithelium; in the mucous membrane are shorter 01 
longer tubular mucous glands (Riess, Kollikcr). The larger the duct the longer these 
glands. Outside the mucous membrane are unstriped muscle cells (Henle), chiefly 
arranged as circular bundles. 

The gall bladder is similar in structure to the large hepatic ducts, except that the 
mucous membrane is much thicker and possessed of folds and villous projections; the 
muscle coat is thick and surrounded by a considerable amount of connective tissue which 
is continuous with the most external layer, viz. the peritoneum. The vascular supply to 
the wall of the gall bladder is very rich, the capillary blood-vessels forming a very dense 
network underneath the single layer of fine columnar epithelial cells lining the inner 
cavity. 

The inner portion of the mucous membrane contains an irregular network of line 
lymphatic vessels (Deutsch). These vessels lead into a network of lymphatic trunks 
possessed of valves and belonging to the outer part of the wall of the gall bladder, vi/. 
to the serous covering. 

PLATE XXXIV. 

Fig. I. From a vertical section through a fold of the mucous membrane of jejunum 
of dog. Magnifying power about 45. 

c. Mucosa containing the crypts of Licberkuhn ; the structure of the villi is only 
indicated. 

?/i. Muscularis mucosae ; here a single (longitudinal) layer. 

.v. Submucous tissue containing the larj/e vessels. 

Fig. II. Part of a crypt of Liebcrktihn, showing the septa extending from the 
membrana propria between the lining epithelial cells ; these latter are only just 
indicated. The lower part of the crypt is cut longitudinally, the upper obliquely. 
Magnifying power about 350. 

Fig. III. Vertical section through the end ol stomach and commencement of 
duodenum of clog. Magnifying power about 45. 

1 and 2. End of the stomach. 

3. The commencement of the duodenum. 

1. Shows the ordinary structure of the pyloric end, as illustrated in Plate XXXIII., 
fig. XXI. 

2. The transition is shown of the pyloric glands into Brunner's glands ; the muscu- 
laris mucosae is here interrupted. This section (2) is somewhat longer in reality than 
here shown. Its length has been reduced on account of want of space. 

N N 



23 2 ATLAS OF HISTOLOGY. 

d. Ducts of the pyloric glands. 

g. The gland tubes cut in different directions. 

m. Muscularis mucosae. 

v. Villi. 

c. Crypts of Lieberkiihn. 

/. A solitary lymph follicle. 

s. Submucosa, containing the glands of Brunner. 

Figs. IV. VI. and VII. copied from Watney, ' Philosophical Transactions/ 
1876. II. 

l 7 ig. IV. Part of a villus of a hedgehog killed during absorption of fat. The 
intestine was hardened in osmic acid. Magnifying power about 450. 

/. Chyle vessel filled with chyle globules. 

The matrix of the surrounding tissue shows the minute (black) chyle granules in 
the reticulum or interstitial substance. 

Fig. V. Part of the plexus myentericus of Auerbach, from the small intestine of a 
new-born child. Magnifying power about 45. 

The details oi structure are shown in fig. X. 

Fig. VI. From the same intestine as figure V., representing a surface view of 
the epithelium covering a villus ; the section had been treated (after osmic acid 
staining) with caustic potash. The chyle granules (black) are contained, not in the 
epithelial cells themselves — seen here endwise as dark shaded polygonal zones — but in 
the interstitial or cement substance between these cells. The clear spaces are the 
openings of goblet cells. Magnifying power about 850. 

Fig. VII. From a section through a villus of duodenum of dog. Magnifying 
power about 550. The figure represents a small portion of the tissue of a villus near 
the summit, which is supposed to lie on the right. 

/. Central chyle vessel ; the nucleated endothelial plates of its lower wall are 
indicated. 

;;/. Unstriped muscle cells running alongside of the chyle vessel towards the apex 

of the villus. 

v. Blood capillary in transverse section. The nucleated endotheloid cells around 

the blood and chyle vessel belong to the stroma of the villus, and together with the fine 

reticulum or interstitial substance between them form its principal constituents. 

Fig. VIII. Copied from Fry's ' Histology,' fig. 109, showing the distribution 
of the lymphatic vessels in the villi, mucous and submucous tissue. Vertical section 
through part of a human Peyer's patch. 

a. Intestinal villi with their central chyle vessel or vessels. 






■/ - ' . 




• 






LYMPHATICS AND BLOOD-VESSELS OF INTESTINE. 233 

b. Lieberkuhn's crypts. 

c, Muscularis mucosae. 

f. Lymph follicle. 

g. Lymph passages around the follicle. 

/. Lymphatic network of the submucosa. 

k. An efferent lymphatic trunk. 

Fig. IX. From a vertical section through small intestine of mouse; the blood- 
vessels are injected with carmine gelatin. Magnifying power about 45. The arterial 
trunks of the submucosa give off the arteries for the villi ; from the dense network of 
capillaries of each villus a vein is seen to emerge near the apex and to pass down into 
the submucosa. 

Fig. X. From the same preparation as fig. V., but more highly magnified, about 



35 



o. 



The placoid enlargements of the nerve branches, filled with very minute ganglion 
cells, are well shown ; the ganglion cells are so closely placed that only their relatively 
large clear nuclei are here seen. The nerve branches give off minute fibres with nuclei 
connected into secondary plexuses. 



PLATE XXXV. 

Fig. XI. Plexus of Auerbach in rectum of toad. From a preparation stained first 
in cloride of gold and afterwards in hematoxylin. Magnifying power about 350. 

n. Nerve branches composed of elementary fibrils. 

g. Large multipolar isolated ganglion cells. 

Fig. XII. Part of a lobule of the pancreas of dog during digestion. Magnifying 
power about 350. 

The gland substance is composed of branched, wavy tubes ; many of them passing 
in an upward or downward direction are cut away transversely or obliquely. 

d. Terminal part of duct or the intermediary part, lined by polyhedral transparent 
epithelial cells. In many instances, however, this epithelium is made up of cells more 
flattened than is here the case. 

a. The alveoli or gland tubes. 

Each epithelial cell of the latter shows very well the distinction into an inner 
'granular 1 and outer homogeneous part containing the nucleus, and staining deeply in 
hematoxylin. 

The cells are separated by a considerable amount of transparent interstitial 
substance. There is hardly any distinct lumen visible in the alveoli, but several nuclei 

N N 2 



ATLAS OF HISTOLOGY. 

indicating the centroacinar cells ; these are transparent and spindle-shaped, but are not 

shown here. 

The transition of the epithelium of the intermediary part of the duct into that of 
the alveoli is represented here as a direct one, but in the preparation it does not appear 
quite so clear ; see the text 

Fig. XIII. From a vertical section through the mucous membrane of the large 
intestine of dog. Magnifying power about 100. 

m. Mucosa containing the crypts of Lieberkiihn ; these are separated by the 
adenoid tissue of the mucosa. 

mm. Muscularis mucosae, consisting of an inner circular (cut longitudinally) and an 
outer longitudinal layer (cut transversely). 
s. Submucous tissue with large vessels. 

Fig. XIV. From a vertical section through the liver of rabbit, after an injection of 
the bile vessels with Berlin blue and of the portal vein and its capillaries with carmine 
gelatin ; showing the greater part of two adjoining lobules. Magnifying power 
about 90. 

a. Interlobular veins. 
h. Central vein. 

The interlobular branches of the portal vein are surrounded by a network of (inter- 
lobular) small bile ducts. These take up the intralobular or bile capillaries forming a 
network, the meshes of which are polyhedral, and correspond to the outlines of the liver 
cells. 

The blue injection did not penetrate farther than about the middle of the lobules, 
that is, midway between the interlobular and central vein. The bile capillaries of the 
tissue surrounding the latter are therefore not injected. The blood capillaries form a 
dense network, more or less radiating from the interlobular to the central vein. The 
liver cells are not represented. 

Fig. XV. A part of a lobule of a similar liver as in the preceding figure, but more 
magnified, about 250. The section is, however, not vertical, but horizontal. In con- 
sequence of this many blood capillaries appear cut transversely. 

b. Bile capillaries. 

c. Blood capillaries, cut longitudinally. 
n. The same in transverse section. 

The liver cells are not shown here, but fill up all the space between bile capillaries 
and blood capillaries. 

Fig. XVI. From a section through a lobule of liver of guinea pig. Magnifying 
power about 450. 



STRUCTURE OF LIVER. 235 

/. Liver cells ; the intracellular and intranuclear networks are very distinct. 

c. blood capillaries injected with Berlin blue. 

Fig. XVII. From a section through liver of guinea pig, showing the transition of 
the interlobular bile duct d through the intermediary part c into the liver cells /at the; 
margin of the lobule. 

The canal of the intermediary part passes into the bile capillaries while its flattened 
cells become continuous with the liver cells. 

Fig. XVIII. From a vertical section through liver of dog, showing the tissue of a 
portal canal in transverse section. Magnifying power about 350. 

a. Artery. 

b. Bile duct lined with columnar epithelium. 
v. Interlobular vein. 

The matrix is formed by bundles of fibrous-connective tissue cut in various direc- 
tions, because running under different angles. 

Fig. XIX. From a lobule of the same liver as fig. XIV. Magnifying power 
about 350. 

b. Bile capillaries between the liver cells. 

c. Capillary blood-vessels. 

Fig. XX. From a vertical section through the liver of pig. Magnifying power 
about 25. 

Five lobules are shown well separated from one another. 

i. Intralobular or central vein. 

s. Interlobular connective tissue or the tissue of the portal canals. 



2$6 ATLAS OF HISTOLOGY. 



CHAPTER XXIX. 

LARYNX AND TRACHEA, BRONCHI AND LUNG. 

i. The Larynx. 

Tjie support of the epiglottis is formed by the reticular or elastic cartilage with its 

fibrous perichondrium, described and figured in Chapter VIII. 

The anterior surface is covered with stratified pavement epithelium; this in no way 
diners from that found in the neighbourhood of the epiglottis, viz. root of tongue or 
pharynx; the mucous membrane underneath the epithelium is fibrous tissue of loose 
texture, containing a network of numerous and wide lymphatics. The part next the epi- 
thelium, the mucosa, is densest and projects in the form of numerous small papilla? into the 
epithelium. The network of capillary blood-vessels is distributed in this superficial 
portion of the mucous membrane. In the deep or submucous portion, that is the one 
close to the perichondrium, are imbedded (in man) small branched tubular mucous 
glands, whose ducts pass in an oblique direction to the free surface, and open here with 
a wide mouth. In carnivorous animals the glands are very rare. The structure of these 
glands and their duct is similar to that of the glands of the pharynx and oesophagus. 

The large lumen of the gland tubes of the epiglottis and other parts of the larynx are lined 
with epithelial cells, which are either : columnar transparent ' mucous ' cells, each with a flattened 
nucleus, like those of the gland tubes in the oral cavity (see p. 196), or : they are columnar cells the 
substance of which is apparently granular and longitudinally striated, the intracellular network being 
dense and pre-eminently longitudinal; the nucleus is spherical and lies in the outer third ; or: the two 
kinds of cells are side by side in the same tube. There are also tubes in which, outside the lining 
'mucous* cells, are 'crescents' of granular polyhedral cells (Heidenhain, Tarchetti, Klein). The 
difference between the two kinds of cells has been described on a former occasion, and it has been 
stated to consist in the fact that the former are in a state of secretion (the intracellular network 
distended by mudgen or mucin) while the latter are in a state of rest or exhaustion. The duct 
is lined with a layer of beautiful columnar cells, and outside this is generally a layer of small poly- 
hedral cells. 

The mucous membrane covering the posterior surface, although similar to that of 
the anterior surface, differs from it in certain essential points, and hence the two may be 
readily distinguished. The differences are as follows : (a) the stratified pavement 
epithelium is distinctly thinner than on the anterior surface ; (&) the mucous membrane 
extends into the epithelium as small papillae, which are shorter and fewer than on the 
anterior surface ; the texture of the mucous membrane is much denser on the posterior 



STRUCTRUE OF EPIGLOTTIS. 237 

surface, and in its superficial parts contains vascular adenoid tissue either diffuse or as 
distinct lymph follicles (Klein, Haidar Kiamil) ; (c) the deep or submucous part is less 
dense in texture and contains many groups of fat cells and small mucous glands. (In 
carnivorous animals these latter are few and almost single tubes, wavy and convoluted). 
They are more numerous than in the anterior membrane and form almost a con- 
tinuous layer. Their ducts penetrate through the mucous membrane and open on 
the posterior surface. The mucous glands are placed closely against the cartilage and 
in some places actually in a depression of this latter. As has been stated on a former 
occasion (p. 52), the cartilage is reticulated, and through its holes the mucous glands 
of one surface are continuous with those of the other; in some parts we tuu\ a mucous 
gland situated in the submucous tissue of the anterior membrane sending its duct 
through a hole of the cartilage to the posterior surface. 

According to Verson the posterior surface of the epiglottis of the new born child is covered with 
columnar ciliated epithelium ; in the adult there are found, according to Davis, islands of stratified 
pavement epithelium amongst the ciliated columnar epithelium of the general surface. 

I have examined the epiglottis of eight children varying in age from two years to twelve, and in 
no single instance have I found the epithelium of the posterior surface other than stratified paveraenl 
epithelium, as described above. Also in carnivorous animals I do not find on the posterior surface 
any other than stratified pavement epithelium, the superficial layers being composed of very 
flattened squamous cells. — E. K. 

Passing from the epiglottis into the larynx the epithelium sooner or later changes 
from stratified pavement epithelium into stratified columnar epithelium, whose superficial 
cells are conical in shape and possessed of cilia (see Chapter II.). 

This change never occurs suddenly, but gradually and in this way : amongst the 
stratified pavement epithelium there appear smaller or larger islands of stratified 
columnar cells, of which the superficial cells are short conical, and in most, hut by no 
means in all, instances possessed of cilia. Further away from the epiglottis these 
islands increase in number and size, so that we find the general surface covered 
with stratified columnar (ciliated) epithelium with a few islands of stratified pave 
ment epithelium amongst them. Ultimately these disappear and stratified columnar 
(ciliated) epithelium only is present. There exist great differences with regard to 
whether the stratified pavement epithelium of the posterior surface of the epiglottis is 
changed into stratified columnar (ciliated) epithelium nearer to or further from the base 
of the epiglottis. The margin of the false vocal cord is covered with stratified pavement 
epithelium (Klein, Davis), so is also the inner surface of the arytenoid cartilage (Davis), 
while in other cases close to the base of the epiglottis the epithelium is an uniform 
columnar ciliated epithelium. 

Over the thyroid and cricoid cartilages the mucous membrane is covered only by 



238 ATLAS OF HISTOLOGY. 

stratified columnar ciliated epithelium of the same nature as that described and figured 
in Chapter II. figs. I. and II. of Plate III. (See also the occurrence of goblet cells in con- 
nection with mucous secretion.) 

The superficial part of the mucous membrane, or the mucosa, is of a tolerably dense 
texture ; it is a meshwork of delicate bundles of fibrous tissue, which in many places 
contains more or less dense adenoid tissue ; this latter tissue occurs chiefly underneath 
the epithelium (Luschka, Verson, Heitler), and contains the ultimate ramifications of the 
blood-vessels, that is a network of capillaries. It occurs either as diffuse adenoid tissue 
or as lymph follicles (Verson, Boldyrew, Coyne). 

Between the epithelium and the mucosa is a distinct basement membrane (see 
below) ; this is always thickest in the deeper parts of the larynx, e.g. over the thyroid 
and cricoid cartilages. 

In these same parts, viz. over the thyroid and cricoid cartilage, the mucosa is 
separated from the next layer or the submucous tissue by a special layer containing net- 
works of longitudinal thick elastic fibres. 

The deeper or submucous part, like the epiglottis, contains numerous mucous 
glands, and groups of fat cells, besides larger vessels and nerve branches. The mucous 
glands are, comparatively speaking, large, compound tubular, and form in many 
places a continuous layer. Their ducts open with wide mouths on the free surface and 
are occasionally lined with ciliated epithelium (Verson). 

The largest mucous glands are found in those parts where the mucous membrane is loose and 
easily folded, e.g. in the false vocal cords. 

The epithelium lining the lower part of the false vocal cord and the ventriculus 
Morgagni, except the part next the margin of the true vocal cord, is stratified columnar 
(ciliated), the mucous membrane is loose in texture and easily folded ; it contains 
numerous mucous glands, and around and between them adenoid tissue either as diffuse 
masses or in the shape of definite lymph follicles (Luschka, Verson, Boldyrew, Heitler). 

Passing from the ventricle on to the true vocal cord the columnar epithelium 
becomes changed into stratified pavement epithelium ; this is thinnest just at the very 
margin ; immediately below this the epithelium becomes again a little thicker, and re- 
mains stratified pavement epithelium for some distance below. This varies in different 
cases. The mucosa is without glands and is a dense tissue chiefly containing networks of 
elastic fibrils and projecting into the epithelium in the form of beautiful regular papillae. 

Between the epithelium and mucosa is a conspicuous basement membrane. 

A short distance below the margin of the vocal cord the mucous glands reappear in 
a loose submucous tissue ; at first they are small and isolated, but soon become larger 
and closer. 



BLOOD-VESSELS OF LARYNX. 239 

With the appearance of the mucous glands, or soon after, the epithelium and the 
mucosa resume again their former characters. 

The distribution of the blood-vessels in the larynx does not differ from the general 
plan of their distribution in other mucous membranes, viz. the larger branches of arteries 
and veins belong to the submucous tissue, while the mucosa contains their ultimate 
ramifications, viz. the network of capillaries. These extend horizontally underneath the 
surface epithelium, except where this latter is stratified pavement epithelium (epiglottis, 
vocal cords) ; in this case the mucosa is possessed of papillae, into each of which extends 
a loop of the capillaries. The mucous glands and lymphatic follicles possess of course 
their own afferent and efferent blood-vessels and capillary networks. 

The lymphatics are very numerous. Generally we find a network of minute lym- 
phatic tubes in the mucosa, leading into a network of larger tubes with valves, and 
situated in the submucous tissue. The most numerous and dense, and at the same time 
largest, lymphatics are found in the anterior membrane of the epiglottis, in the false vocal 
cords, in the ary-epiglottic folds, and in the ventriculus Morgagni. 

The nerve branches found in the submucous tissue are large bundles of medullatcd 
fibres ; isolated medullated and non-medullated fibres may be met with in the mucosa, 
where they are connected in a fine plexus. 

These fibres possess a thick laminated nucleated sheath (Boldyrcw). 

According to Luschka, and also Boldyrew, the nerve fibres terminate in the mucosa 
in the form of end-bulbs. 

On the posterior surface of the epiglottis we meet with taste goblets amongst the 
stratified epithelium (Verson, Schofield, Davis) ; their number increases towards the 
basis, and they are in some instances (dog, Schofield) arranged in rows, and may be 
met with also occasionally on the ary-epiglottic folds and the mucous membrane of the 
inner surface of the arytenoid cartilage, as well as on the true vocal cord (Davis). 

2. The Trachea. 

The structure of the mucous membrane of the trachea is very similar to that of the 
larynx. The different layers described of the latter are continued into the former. 

a) The epithelium is stratified columnar, the superficial cells being ciliated ; its 
minute structure is identical with that of the larynx. 

6) Underneath the epithelium is a homogeneous-looking basement membrane; this 
membrane is very conspicuous in the human trachea on account of its thickness. 

It is permeated by thicker and thinner canals connecting the lymph-canalicular 
system of the mucosa with the intercellular substance of the epithelium. Occasionally 

o o 



24u ATLAS OF HISTOLOGY. 

we find even a greater or smaller part of a lacuna of this lymph-canalicular system ex- 
tending into the membrane. 

c) Underneath the basement membrane is the mucosa ; this consists of a superficial 
and deep section. The former is a reticulated structure, being composed of a meshwork 
of thin fibre bundles, and between them lymphoid cells and flattened connective-tissue 
cells, each with an oval flattened nucleus. In some places, the just-named meshwork is like 
adenoid reticulum, and the mucosa appears then similar to diffuse adenoid tissue. The 
small lacunae of the meshwork are connected with one another by narrower or broader 
channels, and contain both the flattened connective-tissue corpuscles and the lymphoid 
cells ; that is to say, they completely resemble the lymph-canalicular system of other 
connective tissues. 

The deep section of the mucosa is a thin stratum of a network of longitudinal elastic 
fibres, between which lie connective-tissue corpuscles and capillary blood-vessels. 

d) The submucous tissue is loose connective tissue containing the glands, fat tissue 
and the larger blood-vessels and lymphatics, and the nerve trunks. 

The glands are mucus-secreting glands, forming a more or less continuous layer. 
Their structure is in all respects similar to that of the glands of the larynx ; the contrast 
between the two conditions under which the epithelial cells lining the alveoli appear is 
very easily ascertained. In the human trachea we meet with many alveoli, belonging to 
the same gland, which are either lined with * mucous ' cells or with ' granular' epithelial 
cells. As in the larynx, so also here we meet occasionally (especially in cat and dog) a 
gland tube lined with mucous cells, and outside these are ' crescents ' of granular cells 
similar to those of the submaxillary gland of dog (see Chapter XXIV.). 

The duct, and also part of the gland, is in some places embedded in, or surrounded 
by, a lymph follicle. 

The trabecular of connective tissue of the submucosa are continuous both with the 
perichondrium of the cartilage rings and with the tissue between the free ends of these 
latter — that is, the membranous part of the trachea. Here we find also groups of 
bundles of unstriped muscle tissue extending in a transverse (circular) direction between 
the extremities of the cartilage rings. Occasionally we find outside these in addition 
longitudinal muscle bundles ; they are not so numerous in man as in some (carnivorous) 
animals (Verson). 

The mucous glands above mentioned extend not only in amongst the muscle coat, 
but some are placed even outside the latter. 

The outer boundary of the trachea is formed by a layer of fibrous-connective tissue. 
As regards the distribution of blood-vessels, lymphatics, and nerves, the same rela- 
tions exist as in the larynx. 



STRUCTURE OF BRONCHI. 241 



%, Tin-: Bronchi. 



In the bronchi we meet with precisely the same structure as In the trachea. 

The epithelium, as a whole, becomes thinner towards the smaller branches, in 
which it is composed only of one layer of ciliated columnar cells. In the smallest bronchi 
these cells become very short columnar, but retain their cilia to the end — that is, to near 
the alveolar ducts. As in the trachea, so also in the bronchi the epithelial cells arc 
capable of being converted into goblet cells. 

The epithelium lining the mucous membrane of two bronchi belonging to the same order, but 
one of which is distended, the other contracted ad maximum, presents itself in a totally different 
aspect (Klein) ; while in a large bronchus which is contracted the epithelium appears stratified, it is 
but a single layer of cells in a similar bronchus that is much distended. And similarly in tin- 
smallest bronchi the epithelium may appear composed of shorter or longer columnar cells, according 
to whether the bronchus is distended or contracted ad maximum. 

Underneath the epithelium is a basement membrane, which is a single layer of large 
flattened nucleated endothelial cells (Dcbove). 

The mucosa appears as smaller or larger folds, and contains a delicate meshwork of 
minute connective-tissue bundles, between which are seen the connective-tissue cor- 
puscles ; numerous longitudinal elastic fibres, connected into a network, belong to this 

layer. 

In the bronchi of some animals (pig) these elastic fibres attain a very great develop- 

ment, forming a thick stratum of their own. 

Outside this is a more or less continuous circular layer of unstriped muscle cells. 
This layer is very conspicuous, and its thickness varies, of course, whether a bronchus is 
in a distended or contracted state. The depth (or height) of the folds of the mucosa 
entirely depends on the state of contraction of the muscle coat. 

The next layer is the submucous tissue containing small mucous glands. In the 
larger bronchi the connective-tissue trabecule of this layer pass directly into the peri- 
chondrium of the cartilage plates, and into the fibrous coat outside these, viz. the bronchial 
adventitia. The mucous glands generally extend between the cartilage plates into the 
adventitia. Groups of fat cells occur in the submucous tissue as well as in the adventitia. 

Towards the smaller bronchi the glands of the submucous tissue decrease, both in 
size and number, just like the cartilage plates, and in the smallest bronchi the fibrous 
tissue outside the muscle coat contains neither glands nor cartilage. 

In the smaller bronchi the adventitia is very rich in elastic fibrils connected into a 
network. The adventitia of the larger bronchi is connected with the tissue between the 
lobules of the lune-that is, the interlobular septa-while the adventitia of the smaller 



bronchi passes insensibly into the wall of the adjacent alveoli. 



002 



242 ATLAS OF HISTOLOGY. 

The vascular supply of the bronchi is obtained from the bronchial arteries, whose 
ultimate branches supply the mucosa, the muscular coat, the mucous glands and fat tissue 
with special networks of capillaries. In the smallest bronchi, the capillaries of the bron- 
chial wall are directly connected with the capillaries of the adjacent alveoli ; but in the 
larger bronchi the capillaries empty themselves into the bronchial veins only. 

Lymphatic vessels are present as a network of fine capillaries in the mucosa ; they are 
connected with larger tubes with valves situated in the submucous and adventitious tissue, 
the peribronchial lymphatics. In the submucous tissue of the larger as well as smaller 
bronchi are occasionally present smaller or larger lymph follicles (Burdon-Sanderson, 
Klein) ; they extend sometimes as diffuse adenoid tissue into the mucosa, and are 
generally surrounded by a dilatation or a lymph sinus of a peribronchial lymphatic 
(Klein). Small collections of adenoid tissue may be met with in the wall of even the 
smallest bronchi. 

In connection with the nerve branches of the adventitia are small ganglia (Remak, 
Klein, Stirling). 

4. The Lung. 

Like other glands, the lung also possesses a connective-tissue framework in which 
is embedded the parenchyma. 

The framework consists of a capsule, the pulmonary pleura, and in connection with 
it are the septa dividing the parenchyma into lobes and subdividing these again into lobules. 

The capsule consists (in man and the large mammals) of an outer denser layer, 
pleura proper, and an inner looser tissue, subpleural tissue, which passes into the depth 
as the aforesaid septa. 

The pleura is covered on its free surface with an endothelium, whose cells are 
transparent, large, flat, and hyaline when the lung is expanded ad maximum, but 
become smaller, thicker (polyhedral) and granular-looking when the lung collapses (Klein). 
The ground substance is a dense fibrous-connective tissue and in it are networks of elastic 
fibres. Like that of other serous membranes, it contains a lymph-canalicular system, and 
in it branched connective-tissue corpuscles. There exists the same continuity of the 
interstitial substance of the surface endothelium with the lymph-canalicular system, as 
well as of this with the numerous lymphatic vessels (subpleural lymphatics), to be 
described below (Kiittner, Klein), as that occurring in other membranes (see p. 175). 
In some animals (guinea pig) the pulmonary pleura contains a meshwork of broader 
or narrower bands of unstriped muscle cells (Klein) ; the meshes are lymph sinuses, 
communicating with the free surface of the pleura by means of true stomata. 

The subpleural tissue and that constituting the interlobar and interlobular septa con- 



STRUCTURE OF LUNG. 243 

tain lamellae of fibrous-connective tissue, and between them the connective-tissue cor- 
puscles. Numerous lymphatic vessels and lymphatic spaces are here to be met with 
(see below). 

The fibrous-connective tissue surrounding, or rather supporting, the bronchi and 
large vascular trunks (the adventitia) forms a continuity with that of the interlobular 
septa, as already mentioned. 

The parenchyma, consisting of the bronchi, alveolar ducts and alveoli, is divided 
into lobules. 

The small or intralobular bronchi are cylindrical tubes. They divide dichotomously 
into smaller tubes, and ultimately pass into the alveolar ducts (F, E. Schulze, Stieda) 
which take up on all sides of their circumference the lateral alveoli ; the ultimate parts 
of the alveolar ducts are the infundibula (F. E. Schulze), which take up the terminal 
alveoli. The alveoli are spherical or polyhedral in shape, and those belonging to the 
same alveolar duct or infundibulum are separated by much less tissue than tin- alveoli 
of adjacent lobules. 

Passing from a terminal bronchus of man or mammals into an alveolar duct and 
infundibulum, we find that the epithelium becomes reduced to low polyhedral cells with- 
out any cilia : each cell possesses a spherical nucleus. In the alveolar duct and infundi- 
bulum itself we find these polyhedral cells continued as smaller or larger groups, while 
the rest of the lining epithelium is made up of very large flattened transparent cell plates 
of exactly the same appearance as those of an ordinary endothelial membrane. 

From the alveolar ducts and infundibula we trace, into the alveoli, both the small 
polyhedral cells as well as the large flattened cell plates; the latter predominate greatl) 
over the former, there being left only isolated or small groups (two or three) of the small 
polyhedral cells between the transparent placoids lining the alveoli (Elcnx, F, E. 
Schulze and others). In the lung of cat the number of such polyhedral cells is greater 
than in the lung of other mammals. They are easily perceived both in the fresh state 
as well as after reagents, especially after staining with nitrate of silver, being conspicu- 
ous by their 'granular' appearance, and by being smaller and much thicker than tin 
others, viz. the placoids. 

Except in size and appearance the two kinds of cells are identical, both being 
epithelial cells derived from the hypoblast of the embryo. At first sight it seems as if 
the two kinds of cells were essentially different, the one being a continuation of the 
polyhedral epithelial cells lining the terminal parts of the bronchi, the other of the sub- 
epithelial endothelial membrane mentioned above. And this has indeed been asserted 
to be the case (Debove) ; but there can be no doubt that in the embryo this distinction 



244 ATLAS OF HISTOLOGY. 

does not exist, and in the lung of the foetus that has not breathed yet, the alveoli are lined 
only by one kind of cells, viz. by small polyhedral granular-looking cells ; only after 
respiration has begun and the alveoli have become expanded and remain so, .we find the 
two kinds of cells (Kuttner). But also in the adult a transition of the one kind of cells into 
the other can be observed, for during a maximum expansion of the alveoli most of the 
small polyhedral granular cells become flattened transparent placoids, which resume 
again their previous nature when the alveoli collapse. 

In the alveolar ducts, infundibula, and alveoli there appear larger or smaller 
circular or angular openings (Buhl and others) between the lining cell plates, similar to 
stomata (pseudo-stomata) in serous membranes. They are conspicuous only in the 
distended alveoli ; when the latter are collapsed they are reduced into the smallest 
points or stigmata. As has been mentioned on a previous page in connection with the 
serous membranes, these pseudo-stomata correspond to the interstitial substance 
between the placoids lining the lumen of the alveoli. They lead into the lymph- 
canalicular system of the alveolar wall. 

The wall of the alveolar ducts and infundibula is made up chiefly of unstriped 
muscle cells, running in a circular manner ; there is present a very small amount of 
fibrous tissue, and in it branched connective-tissue cells in their respective lymph- 
canalicular system. An uniform network of elastic fibres increases the thickness of the 
wall. It is barely necessary to add that the connective tissue, the elastic fibres, and the 
branched cells are continuations of the same elements of the ultimate bronchi. In the 
wall of the alveoli we meet chiefly with a network of broader and finer elastic fibres and 
a dense network of capillary blood-vessels, the latter being in close contact with the 
epithelium lining the alveolar cavity. Between and outside the capillaries we find a 
network of branched cells in their respective lymph-canalicular system, embedded in a 
homogeneous ground-substance ; the branched cells with their processes— or the lymph- 
canalicular system respectively — penetrate between the alveolar epithelium, where they 
identify themselves with the interstitial substance (Klein, Kuttner). 

Bands of unstriped muscle cells are absent from the greater part of the alveolar 
wall ; they are seen to pass from the alveolar ducts and infundibula a short distance 
into the alveolar wall. 

As mentioned above, the tissue separating the alveoli of adjacent lobules is greater 
in amount than that between alveoli belonging to the same alveolar duct or infundibulum, 
and in the former case we see besides elastic networks also a certain amount of fibrous- 
connective tissue, belonging to the interlobular septa. 

The most important part of the alveolar septa are the capillary vessels. They 
are connected into an exceedingly dense network, which is intermediary between the 



CAPILLARY VESSELS OF ALVEOLI OF LUNG. 245 

branches of the pulmonary artery and pulmonary vein. Not each alveolus belonging to one 
and the same lobule has its own afferent arteriole, efferent vein, and capillary network, 
but a number of neighbouring alveoli possess a common vascular supply ; the afferent 
arteriole and efferent vein or veins join the capillary network generally at opposite sides ; 
the network of capillaries, according to the peculiar globular nature of the alveoli, 
possesses, as it were, a honey-combed arrangement. The individual capillaries are 
either straight or more or less wavy ; in the contracted lung they are of course very 
wavy, and quite close. The capillaries belonging to the septa between adjacent alveoli 
are in many instances more or less twisted, so as to approach now the cavity of the 
one, now again that of the other alveolus. The structure of the capillary blood-vessels 
in no way differs from that of other organs. The branched connective-tissue cells with 
their processes, mentioned above, are seen entwining and crossing the capillaries. 

Near a bronchus, and near the pleura, the alveolar capillaries anastomose with the 
capillaries of these organs : that is to say, with the capillaries of the bronchial artery. 
This is, however, denied by Cohnheim and Litten, but reaffirmed by lloyer, Koster, 
and others. 

The large arterial and venous branches are situated in the interlobular connective 
tissue, which is continuous with their adventitia. Of interest is the arrangement of the 
muscle coat in the branches of the pulmonary artery, the (circular) muscle coat not 
being a continuous one, but interrupted from place to place (Klein), so that at these 
points the adventitia is in immediate contact with the intima. This state is very well 
shown in the lung of guinea pig. 

The lymphatics are very numerous (Wywodzoff, Sykorski, Klein, Kiittner, and 
others). They are arranged in the following three systems : (a) the subpleural 
lymphatics (superficial lymphatics, Wywodzoff) forming a dense plexus of lymphatic 
vessels, many of which contain valves. Their wall is, as usual, a single endothelial 
membrane. These subpleural vessels take their rootlets in the pleura itself, but 
especially in the Iymph-canalicular system of the walls of the alveoli next the pleura. 
The meshes of this plexus correspond, on the whole, to the outlines of the alveoli, 
but there are many places where the vessels are much closer. 

In the lung of cattle the vessels of the subpleural plexus form more or less separate 
sections, according to the individual lobules, and the vessels of each such section have 

a stellate arrangement (Roy). 

In man and many mammals this plexus of subpleural vessels sends efferent trunks, 
through the ligamenta pulmonum, directly to the bronchial glands, but there are 
always numerous vessels that pass from the subpleural plexus through the interlobular 
connective tissue to join (b) the perivascular lymphatics. These have their rootlets 



246 ATLAS OF HISTOLOGY. 

in the lymph-canalicular system of the wall of the alveoli. These vessels accompany 
the branches of the pulmonary artery and vein, and the larger trunks possess valves. 
In some places the perivascular lymphatics more or less completely invaginate the 
arterial or venous branches, in others the lymphatics form a dense network of inter- 
communicating sinuses in the sheath of the large branches of the pulmonary artery 

(Klein). 

(c) The peribronchial lymphatics, which have been mentioned previously as the 
deep lymphatics of the bronchi, to whose adventitia they belong, anastomose freely with 
the perivascular lymphatics and run with them, in the form of a plexus of lymphatic 
trunks with valves, through the interlobular and interlobar connective tissue towards the 
bronchial glands. 

The rootlets of the subpleural and the perivascular lymphatics, as mentioned already, 
lie in the alveolar walls, that is in the lymph-canalicular system described on a former 
page. The lacunar of this (lymph-canalicular) system are situated between the capillary 
blood-vessels, and their canaliculi cross these latter in many directions. During the 
expansion of the lung (inspiration), the lymph-canalicular system, as well as the 
lymphatic vessels, become distended, and there is caused hereby, naturally, a certain 
suction, in consequence of which formed or fluid matter, that happens to be present 
in the alveolar cavities, will readily penetrate from the latter into the lymphatic vessels. 
The above-described direct connection of the lymph-canalicular system with the inter- 
stitial substance between the epithelial cells lining the alveolar cavity is of great import- 
ance in this process. Sykorski, and afterwards Ktittner, demonstrated very beautifully 
the passage of pigment matter that had been inspired into the bronchi and alveoli during 
life (dog, cat, rabbit) through the interstitial substance of the lining epithelium into the 
lymph-canalicular system, and hence into the lymphatic vessels, all parts being very well 
injected. Inflammatory products present in the alveolar cavities readily find their way 
into the efferent lymphatics. The migratory lymph cells (pus-corpuscles) of inflamma- 
tion are supported in this by their amceboid movement. 

A more or less similar success was achieved by Ruppert, Schottelius, and v. 
Ins. Schestopal injected the lymphatic system of the frogs lung by introducing pig- 
ment matter into its cavity. The result is the same as in the experiments of Ktitt- 
ner on mammals, viz. the pigment matter is contained in the interstitial substance 
of the lining epithelium, in the lymph-canalicular system, and, finally, in the lymphatic 
vessels. 

Coal particles of a smoky atmosphere, when inhaled for some time, penetrate into the 
lymph-canalicular system of the alveolar walls, as well as into the lymphatics of many 
parts of the lung. They are especially distinct in the subpleural lymphatics and the 









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ABSORPTION BY THE LYMPHATICS OF THE LUNG. 2 A1 

lymphatics of the interlobular connective tissue (Knauff, Wittich, Buhl, Rindfleisch, 
and others). 

Also other particles (dust of every description, septic matter, contagious particles, etc) 
may penetrate into the lymph- canalicular system, either as such-viz. merely in consequence of the 
above suction-or they are carried there by lymphoid cells (inflammatory products), which had 
taken them up previously (see Chapter I.). 

Just as much as the inspiratory movement of the lung aids absorption, so the 
expiratory movement produces a contraction of the lymphatics, and therefore a pro- 
gression of the contents of the latter towards the bronchial glands. 

PLATE XXXVI. 

Fig. I. From a longitudinal section through the innermost part of the mucous mem- 
brane of the trachea of a child. Magnifying power about 300. 

a. Stratified columnar epithelium ; the superficial conical cells are ciliated. 

b. Basement membrane, perforated by fine vertical canals of the lymph-canalicular 
system underneath. 

c. The inner section of the mucosa, containing capillary blood-vessels. 

d. The layer of longitudinal elastic fibres connected into a network. 

e. First section of the submucous tissue with large vessels. 

Fig. II. From a vertical section through the stratified pavement epithelium cover- 
ing the mucous membrane of the posterior surface of the epiglottis of a child. Magnify- 
ing power about 300. 

s. Free surface. 

d. Inner surface attached to the mucosa. 

Fig. III. From a section through a mucous gland of epiglottis of child, showing 
gland tubes cut in various directions. Magnifying power about 450. 

a. A gland tube cut transversely ; the epithelium lining it is in a state of rest. 

b. A similar tube, whose epithelium is in a state of secretion. 

c. A tube cut obliquely ; in the lower part the epithelium is in a state of rest, in the 
upper in a state of secretion. 

Fig. IV. From a transverse section through the epiglottis of a child. Magnifying 
power about 45. 

a. The stratified pavement epithelium of the posterior surface. 

b. The mucous membrane containing mucous glands. 

c. The elastic cartilage. 

d. The mucous glands of the anterior surface. In this instance a duct is seen to 
pass through the posterior mucous membrane. 

p p 



24 g ATLAS OF HISTOLOGY. 

e. The mucous membrane of the anterior surface contains numerous lymphatics, 
cut here in various directions. 

/ The stratified pavement epithelium of the anterior surface. 

/. Lymph follicle. 

Fig V. From a longitudinal section through the ventriculus Morgagni of a child. 
Magnifying power about 45. In order to correspond to the natural position the drawing 
should be reversed. 

a. The true vocal cord, covered with stratified pavement epithelium. The mucosa 
contains dense elastic tissue. 

6. The false vocal cord ; its margin is covered with stratified pavement epithelium, 
towards the epiglottis the epithelium is stratified columnar (ciliated), intermixed with 
islands of stratified pavement cells. These minute details are not shown here on 
account of the low power under which the drawing is made. The mucous membrane 
contains numerous mucous glands 

c. A nodule of elastic cartilage in the true vocal cord. 

d. Ventricle lined with ciliated columnar epithelium. 

/. The mucous membrane next the epithelium, being one continuous mass of 
adenoid tissue. The outer section of the mucous membrane containing mucous glands 
and striped muscle (upper portion of thyro-arytenoid muscle) is not represented. 

ni. Striped muscle fibres in transverse sections, the lower portion of the thyro- 
arytenoid muscle. 

Fig. VI. From a longitudinal section through the same trachea as fig. I., but 
under a low power, so as to show the whole thickness of the mucous membrane. 
Magnifying power about 45. 

a. The stratified columnar (ciliated) epithelium. 

b. The basement membrane. 

c. The inner section of the mucosa. 

d. The network of longitudinal elastic fibres. 

e. The submucous tissue, containing mucous glands and large vessels. 

f. Portions of the (hyaline) cartilage rings in transverse section. 

g. Fat cells. 

Fig. VII. From an oblique section through the trachea of foetus. Owing to the 
obliquity of the section, several cartilage rings (stained deep purple) are included in 
the section. The trachea is much shrunk and placed in folds. Magnifying power 
about 25. 

e. The ciliated columnar epithelium. 

m. The unstriped muscle tissue of the posterior membranous part. 









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je 






j 



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XI 







Sl^RUCTURE OF ALVEOLI OF LUNG. 249 

The mucosa contains mucous gland tubes. 

Fig. VIII. From a section through the lung of cat, stained first with nitrate of 
silver and then with hematoxylin. 

a. Alveoli lined with large flat transparent nucleated epithelial cells ; amongst them 
are small polyhedral nucleated cells more deeply stained ; they are especially well shown 
where the alveolar wall is seen in profile. Between the large flat cells are smaller or 
larger clear spaces corresponding to pseudo-stomata. 

s. Alveolar septa. 

s. A group of small polyhedral epithelial cells continued from the bronchus. 

e. Alveolar duct in section. 

i. The circular muscle coat. 

Fig. IX. From a section through lung of a child whose pulmonary artery had 
been injected with Berlin blue, Magnifying power about 25. 

a. The afferent and efferent vessels ; on account of the low power it is not possible 
to recognise which is the branch of the pulmonary artery and which of the vein ; but 
under a high power it can be ascertained that the upper corresponds to the artery. 

b. The arrangement of the network of capillaries according to the individual 
alveoli is easily recognised. 



PLATE XXXVII. 

{Copied from Kleiris i Anatomy of the Lymphatic System.' II) 

Fig. X. Section through a large bronchus of the lung of guinea pig ; the blood- 
vessels had been injected from the pulmonary artery. The injection had escaped 
through the lymphatics, which are here distended. The section is oblique, and there- 
fore in the upper part of the figure the bronchial wall is viewed more or less from its 
external surface. 

a. Ciliated epithelium lining the inner surface. 

b. Muscular coat. 

c. A duct of a mucous gland. 

d. Veins. 

e. A branch of pulmonary artery. 
g. Perivascular lymphatics. 

//. Peribronchial lymphatics, anastomosing with the former. 

i. A lymphatic follicle. 

k. Cartilage. Magnifying power about 50. 



250 ATLAS OF HISTOLOGY. 

Fig. XI. From a section through a guinea pig's lung that had been injected 
with nitrate of silver. 

a. Branch of pulmonary artery. 

b. A lymphatic vessel, in connection with 

c. Interalveolar lymph spaces, i.e. the lymph-canalicular system. Magnifying 
power about 150. 

Fig. XII. From the same lung as the preceding figure, showing the lymph- 
canalicular system of the alveolar wall as viewed from the surface. 

Fig. XIII. Surface view of distended subpleural lymphatics (injected) of guinea pig. 

a. Large trunks with valves. 

b. Branches emerging from the depth, i.e. from the interalveolar tissue. Magni- 
fying power about 90. 



251 



CHAPTER XXX. 

THE URINARY ORGANS. 

The Kidney. 
The framework of the kidney of man and mammals consists of (a) the outer capsule ; 
(6) the membrane lining the pelvis and calices ; (c) the tissue passing from the calices 
into the parenchyma of the kidney as the carrier of the large blood-vessels ; (d) the 
connective tissue of the parenchyma itself. 

a) The capsule is composed of fibrous- connective tissue more or less of a lamellar 
arrangement, with the corresponding flattened endotheloid connective-tissue corpuscles 
between the lamellae. A thin deep portion of the capsular tissue is much looser and 
more delicate than the rest; its bundles penetrate between the tubes of the peripheral 
part of the cortex, chiefly in connection with the vascular branches running between 
the latter (cortex) and the capsule. According to E berth there exists a plexus of 
unstriped muscle cells underneath the capsule of the human kidney. 

b) The membrane lining the pelvis and calices is, like the one forming the wall 
of the ureter, covered on its internal free surface with stratified transitional epithelium 
(see below). Underneath this epithelium is a dense feltwork of connective tissue with 
the corresponding connective-tissue corpuscles. This stratum is the mucosa, and it passes 
insensibly into the loose outer coat or submucosa, composed chiefly of trabecular of 
connective tissue and a few elastic fibres ; its outer section contains a greater or smaller 
amount of fat-cell tissue, while its inner section includes numerous bundles of unstriped 
muscle cells, arranged in a longitudinal and circular layer and continuous with the muscular 
coat of the ureter. On the papillae only circular muscular fibres are met with (Hcnlc). 

Paladino, Sertoli, and especially Egli, described in the pelvis of the kidney of the horse small, 
simple or branched gland tubes lined with a single layer of columnar epithelial cells ; also in the pelvis 
of the human kidney Egli observed, but not constantly, gland tubes similar to sebaceous follicles. 

c) The connective tissue of the submucosa above mentioned penetrates, together with 
the large vascular trunks, into the parenchyma, at the boundary of the cortex and medulla. 
It also carries with it longitudinal muscular bundles; they retain the same direction while 
accompanying the vascular trunks, viz. more or less parallel to the surface of the kidney. 

d) The connective tissue of the parenchyma differs very greatly in the different parts 

QQ 



2 5 2 ATLAS OF HISTOLOGY. 

of the latter. Around each Malpighian corpuscle there is always present an appreciable 
amount of fibrous-connective tissue (Ludwig and Zawarykin) with the corresponding 
connective-tissue cells ; it is more abundant in the young kidney than in the adult. 
This connective tissue forms a continuity with the connective tissue around the afferent 
arteriole, further with that around the interlobular artery, and finally with the connective 
tissue surrounding the large arterial trunks situated at the boundary between the cortex 
and medulla. 

A small amount of fibrous-connective tissue may be traced from the last-mentioned 
trunks on the arteriolar rectal into the boundary layer of the medulla (see below). 

The papillary part of the medulla (see below) contains a great amount of fibrous- 
connective tissue (Henle) separating the urinary tubules ; it increases in amount towards 
the apex of the papilla, and becomes continuous with the fibrous tissue of the surface of 
the papilla. 

The boundary layer between the medulla and the cortex possesses only a scanty 
intertubular connective tissue : this tissue consists of hyaline honey-combed mem- 
branous structures — the supporting tissue of the urinary tubules and the capillary blood- 
vessels — to which are applied from place to place flattened branched or spindle-shaped 
connective-tissue cells, each with an oval nucleus generally placed transversely to the 
long axis of the urinary tubules (Schweigger-Seidel). 



The constituents of the parenchyma are the urinary tubules. They commence 
with a caecal extremity in the Malpighian corpuscles and terminate with an opening on 
the free surface of the papilla. 

Owing to the peculiar arrangement of the tubules, a vertical section through the 
kidney exhibits three distinct regions : the cortex, the boundary layer (Grenzschichte) of 
Ludwig, and the papillary portion, the two last forming the medulla. 

Each papilla, with the section of boundary layer belonging to it, forms a pyramid of Malpighi. 

The papillary portion is uniformly vertically striated, the striae being due to 
urinary tubules and blood-vessels, all of them running parallel, straight and vertically to 
the apex of the papilla. The boundary layer is also uniformly striated, the striae having 
a parallel and longitudinal course, but they are grouped in columns, alternately opaque 
and light, the former being composed of more or less straight urinary tubules, the 
latter of straight blood-vessels (vasa recta). The cortex shows, in a uniform labyrinth of 
convoluted tubules, regularly disposed vertical, straight columns radiating towards the 
boundary layer ; being the direct continuations of the opaque columns (urinary tubules) 
of this latter, they are called the medullary rays. 



RELATION OF DIFFERENT PARTS OF KIDNEY. 253 

At the commencement of the cortex (next the boundary layer) the medullary rays 
are of about the same thickness as the aforesaid opaque columns of the boundary layer, 
but they diminish gradually towards the periphery of the cortex and cease altogether at 
some distance from the outer capsule; hence each of these medullary rays is conical in 
shape, its apex lying in the periphery of the cortex and its base merging into the base 
of the medulla : they represent what are called the pyramids of Ferrein. 

Taking the vertical diameter of both cortex and medulla together as 10, the relative 
proportions of the above three sections, viz. cortex, boundary layer, and papillary portion, 
are about 3*5 : 2-5 : 4. 

In the human kidney and in that of other mammals Malpighian corpuscles are 
present only in the parts of the cortex containing convoluted tubules, i.e. in the labyrinth 
between the medullary rays, except the most external and most internal layer of the cortex, 
that is near the capsule and near the boundary layer. In both places, but especially in 
the former, there is a layer of appreciable thickness without any Malpighian corpuscles. 

Taking the vertical diameter of the cortex as 7, we find a layer of the thickness of [ next the 
capsule, and one of o*8 next the boundary layer, without any Malpighian corpuscles, as shown in 
the diagram 1 of Plate XXXVIIa. as a and 0,. 

Every urinary tubule, from its beginning in the Malpighian corpuscle to its opening 
on the surface of the papilla, can be divided into several distinct sections ; these differ 
from one another very markedly in location and structure. 

In diagram 1 of Plate XXXVIIa. these different sections are well marked : 

1. The Malpighian corpuscle, being a spherical caecal commencement of the 
urinary tubule. 

2. The neck, a short narrow constriction, through which the Malpighian corpuscle 
passes into : 

3. The proximal convoluted tubule. This is of considerable length and finally 
passes into : 

4. The spiral tubule (Schachowa). This is not situated any more in the labyrinth, 
but forms part of the medullary ray. 

These four sections belong to the cortex a. Passing from the cortex into the 
boundary layer 1;, the spiral tubule becomes suddenly very fine and straight as : 

5. The descending limb of Henle's loop. This is continued into the beginning 
of the papillary section c, where it forms : 

6. The loop itself. When entering the boundary layer again, it becomes suddenly 
enlarged and slightly wavy, forming thus : 

7. The first thick portion of the ascending limb of Henle's loop. 

8. About midway in the boundary layer this tubule becomes again narrower and 

QQ 2 



254 ATLAS OF HISTOLOGY. 

assumes a spiral course, thus forming a distinct section as the spiral part of the ascend- 
ing limb. 

9. Now the tubule enters again the cortex, and becoming narrower and more or less 
straight, or slightly wavy, ascends in the medullary ray. After a longer or shorter 
course, during which it may undergo a slight variation in thickness, it leaves the 
medullary ray and enters the labyrinth, winding its way amongst the convoluted 
tubules as : 

10. The irregular tubule, which is very irregular in outline, breadth and course. It 
passes into : 

11. The intercalated segment (Schaltstuck) of Schweigger-Seidel, this being the 
distal convoluted tubule of exactly the same nature as the above-named third section, 
viz. the proximal convoluted tubule. After a longer or shorter course it passes into : 

12. The curved part of the collecting tube, a narrow tube of a wavy, curved course 
having to find its way through the labyrinth. It joins other similar tubes and forms : 

13. The straight part of the collecting tube of the cortex : this tube forms part of 
the medullary ray. 

14. Now the collecting tube enters the boundary layer, and while passing through it 
increases in breadth but remains straight. It enters finally the papillary portion as : 

15. The large collecting tube, or tube of Bellini, a large straight tube joining other 
collecting tubes. 

16. Having by anastomosis with similar tubes become greatly enlarged, it opens as 
one of the ' ducts ' with its ' mouth ' on the free surface of the papilla. 

From the foregoing description and the diagram 1 of Plate XXXVIlA., it will be seen 
that the Malpighian corpuscle, with its neck (1 and 2), the proximal convoluted tubule (3), the 
spiral tubule (4), the straight narrow part of the cortical ascending limb of Henle's loop (9), the 
irregular tubule (10), the intercalated segment of Schweigger-Seidel or the distal convoluted 
tubule (11), the curved part of the collecting tube (12), and the next following straight part of the 
collecting tube (13) belong to the cortex. Amongst these the sections marked 1, 2, 3, 10, 11 and 
12 belong to the labyrinth, whereas 4, 9 and 13 form the medullary ray, section 4, i.e. the spiral 
tubule, being the most conspicuous feature in it. Owing to the collecting tubes of the medullary 
rays originating through the confluence of several (curved) collecting tubules, it follows that 
the number of the former is much smaller than the other kinds of tubes forming the medullary 
rays, viz. the spiral tubules (4) and the ascending limbs of Henle's tubes (9), the two latter being 
of course equal in numbers. The descending limb of Henle's loop (5), the first thick portion of 
the ascending limb (7), the next following spiral part (8), and the collecting tube (14), belong to 
the boundary layer of the medulla and form at the same time the continuation of the medullary 
ray; while Henle's loop itself (6), the large collecting tubes (15), and the ducts belong to the 
papillary portion of the medulla. 

The line of demarcation between the cortex and the boundary layer is formed by the limit 
to which convoluted tubes extend and by the transition of the spiral tubule (4) into the de- 
scending limb of Henle's loop (5), and of the spiral portion of the ascending limb (8), into the 
straight narrow cortical part of the same (9). The line of demarcation between the boundary 



DISTRIBUTION OF RENAL TUBULES. 



2 55 



layer and the papillary part is formed by the transition of the loop itself (6) into the first thick 
part of the ascending limb (7). 

Proximal and distal convoluted tubules (3 and 1 1), irregular tubules (10), and curved collecting 
tubes (12) are met with in all parts of the labyrinth, including the peripheral layer of the cortex 
(a in the diagram), viz. the one mentioned as free of Malpighian corpuscles. The convoluted tubules 
of this region, viz. next the capsule of the kidney, form more or less distinctly looplikc 
curvatures. The length of the different sections of the urinary tubules in the cortex is subject to 
very great differences, for to a Malpighian corpuscle, situated in the periphery of the cortex, and 
whose proximal convoluted tubule extends even into the layer a t must necessarily belong a spiral 
tubule (4) of much greater length than the one that belongs to a Malpighian corpuscle situated 
near a v And similarly the straight part of the cortical ascending limb of Heine's loop (9), leading 
to an irregular tubule (10) that is situated in the peripheral layer a, must be very much longer than 
one leading to an irregular tubule that is situated near the layer a { . 

The neighbouring Malpighian corpuscles and the different sections of neighbouring- 
convoluted tubules bear in so far a certain relation to one another, as their spiral tubules, 
descending and ascending limbs of Henle's loops, and collecting tubules keep together in 
the same medullary ray and its prolongation into the boundary layer. Hence each 
'duct' may be considered as the apex of a small cone whose long axis lies in the 
medullary ray ; its basis is in the cortex, and is formed by the Malpighian corpuscles 
and the corresponding convoluted irregular and curved tubules above named. These 
cones are the primitive cones of Ludwig, and the medulla and cortex may thus be con- 
sidered as composed of as many cones as there are ' ducts.* 



The above sixteen divisions of the urinary tubules differ from one another in 
structure in a marked manner. 

1. The Malpighian corpuscle. This is composed of the capsule of Bowman and the 
glomerulus. The capsule of Bowman is the saccular commencement of tin: urinary 
tubule ; it consists of a hyaline membrana propria, thickened on the outside by a varying 
amount of fibrous-connective tissue, mentioned on a former page. The inner surface of 
the capsule is lined with a single layer of flattened epithelial cells, each with a flattened 
oval nucleus. In the young state these epithelial cells are less flattened, being more or 
less polyhedral. 

The glomerulus is a network of convoluted capillary blood-vessels, grouped into 
two, three, or more conical lobules. These lobules occupy the cavity of the capsule of 
Bowman, without, however, filling it. The space between the surface of the glomerulus 
and the capsule varies greatly in the normal and abnormal conditions, according to the 
different states of secretion, being dependent on the amount and nature of the 
secretion present in it. The capillary blood vessels of the various lobules of the 
o-lomerulus are held together by a homogeneous connective tissue, in which are 



256 ATLAS OF HISTOLOGY. 

embedded flattened nucleated branched connective-tissue cells (Axel Key). The lobules 
of the glomerulus are covered with a membrane composed of a single layer of nucleated 
epithelial cells, which membrane dips in even between the capillaries of a lobule 
(Heidenhain). 

The epithelial covering of the glomerulus is continuous with the epithelial lining of 
Bowman's capsule ; this condition is due to the fact that, in the development of the 
Malpighian corpuscle, the extremity of the foetal urinary tubule becomes invaginated by 
the progressive growth of the embryonal glomerulus. Bowman's capsule appears thus 
inflected over the latter. 

The younger the Malpighian corpuscle the more distinct is the epithelium covering 
the glomerulus ; in the human fcetus it is made up of polyhedral or even short 
columnar cells, at a time when the epithelium lining Bowman's capsule is already much 
flattened, as is well shown in fig. 2 of Plate XXXVI Ia. 

The glomerulus of each Malpighian corpuscle is connected with an afferent and 
efferent vessel ; both these lie closely side by side where they join the glomerulus, and 
form, as it were, the peduncle of this latter. 

The Malpighian corpuscles vary in size; they are generally larger in the parts of the cortex 
nearest the boundary layer, and decrease in size towards the surface of the cortex (Drasch). 

2. Opposite this peduncle, Bowman's capsule passes into the urinary tubule through 
a short narrow neck. The flattened epithelium lining the former is not always easily fol- 
lowed into the latter, and consequently the cavity of the neck, which of course is a con- 
tinuation of the space of the Malpighian corpuscle, appears as if without any epithelial 
lining, the membrana propria alone forming the wall of this part. 

3. Immediately after the neck the urinary tubule becomes enlarged and much con- 
voluted, and this has been above referred to as the proximal convoluted tubule. Its 
limiting membrana propria is a direct continuation of the hyaline capsule of Bowman, 
and it is lined with a single layer of epithelial cells. The tube possesses a distinct 
cavity of about one third or more of the whole diameter of the tube. 

The membrana propria remains the same through all sections of the urinary tubule 
in the cortex and medulla. There are in some places oblong flattened nuclei to be 
recognised in this membrane, as if it were composed of endothelial plates ; minute 
septules containing here and there an oblong or angular nucleus pass from the mem- 
brana propria in amongst the epithelial cells lining it, similar to what is the case in gland 
tubes of other organs, as described in previous chapters. 

Now, with the exception of the descending limb of Henle's loop (5), the loop itself 
(6) and all parts of the collecting tube (12, 13, 14, 15 and 16), the epithelial cells lining 
the membrana propria of the other sections are made up of a substance containino- 



STRUCTURE OF EPITHELIUM OF RENAL TUBULES. 257 

more or less complete rods or fibrils, placed vertically to the long axis of the tube. This 
fact was first pointed out by Heidenhain and is easily verified in the kidney of most 
mammals and man, especially when prepared with chromate of ammonia. These rods 
or fibrils, as already shown by Heidenhain, are generally most distinct in the outer part 
of the epithelial cell, that is the part near the membrana propria, while the inner part 
appears more uniformly and finely granular. But the rods or fibrils, when looked at 
from the surface, are clearly connected into a network (Klein), so that they are more 
probably septa of a honey-combed network seen in profile. 

Wherever the cells show these ' rods,' their (cells) shape is polyhedral, or in some 
parts, to be presently mentioned, more or less flattened ; many of them are angular 
and possessed of minute prolongations wedged in between neighbouring cells. 

In the proximal convoluted tubule (3), now under consideration, the epithelial cells 
are, on the whole, polyhedral or short columnar. They are of unequal size, some being 
broader and longer than others. The sides of the cells arc not straight, but cither con- 
vex or concave, the convex sides of one cell fitting into the concave ones of its neigh- 
bours. The outer angles, viz. those next the membrana propria, possess in some cells 
short angular prolongations. 

As already mentioned, they show distinct vertical striation, especially in the outer 
part of their substance. 

A spherical nucleus is found in each cell in about the middle of its substance. 

The first epithelial cells immediately next the neck are much shorter than the fol- 
lowing ones, and this produces the appearance of a sudden tapering off of the epithe- 
lium towards the neck. 

The height of the lining epithelial cells and the lumen of the tube vary consider- 
ably in the convoluted tubules in different kidneys of man and mammals and in different 
parts of the same kidney, for in some instances the epithelial cells are considerably 
larger, being cylindrical with convex free surface, and the lumen consequently smaller than 
in others. The substance of the cells is in these tubes more opaque than in those with 
polyhedral cells and large lumen. Judging by analogy from the experience of Strieker 
and Spina, this is probably due to a difference in the state of function, the latter ap- 
pearance, viz. the cylindrical cells, the small lumen and the lesser transparency of the 
tubule as a whole, indicating an active state of secretion. 

4. The spiral tubule, first pointed out by Schachowa as a definite section, possesses 
a more or less spiral course in the medullary ray ; its thickness and the relation of its 
more or less columnar epithelium and lumen are about the same as in the convoluted 
tubule, just described. The striation of the epithelial cells is very distinct in the first 
part of the tube, but gradually, as the boundary layer is approached, it becomes less so, 



25 8 ATLAS OF HISTOLOGY. 

the substance of the epithelial cells assuming a homogeneous aspect. In many instances 
the substance of the epithelial cells is in this section, on the contrary, of a reticular nature, 
the meshes being of a relatively large size. 

As regards the first part of the spiral tubules, a distinction may be also noticed 
between tubes possessing a large lumen lined with comparatively transparent, short 
polyhedral epithelial cells, and tubes whose lumen is much smaller, the epithelium 
more opaque, and its cells more columnar. 

The irregularity and inequality in the epithelial cells lining this tube are still more 
conspicuous than in the preceding section, especially in the first part of the former. 
These irregularities lead to a distinction into thin columnar cells with concave sides, and 
broader spheroidal cells with convex sides and convex free surface, and hence pos- 
sessing a fungoid shape, * fungoid cells ' of Schachowa. 

5 and 6. The descending limb of Henle's loop and the loop itself are exceedingly 
thin tubes, whose membrana propria is lined with a layer of very flat transparent cell 
plates, each possessed of an oval flattened nucleus. These tubes resemble in size and 
transparency capillary blood-vessels, but differ from them by the greater number of their 
nuclei and by the presence of a membrana propria outside the layer of cell plates. 
But this distinction into a membrana propria and lining cell plates is not always easily 
made. 

7. As mentioned above, just where the ascending limb of Henle's loop enters the 
boundary layer it becomes suddenly enlarged, but reaches its greatest breadth a little 
distance from its entrance into this layer. The epithelial lining is again composed of 
polyhedral cells with very distinct vertical rods, when viewed in profile ; each cell is pos- 
sessed of a spherical nucleus situated in the innermost part of the cell, i.e. next the 
lumen. This latter is very conspicuous. The outline of the tube is not straight, and its 
breadth varies slightly from place to place. 

8. About midway in the boundary layer the tube becomes again narrower and fol- 
lows a more or less spiral course, hence it may be called the spiral portion of the ascend- 
ing limb. Its outline is irregular, and it differs from the preceding by being narrower, 
and its lumen very small, just perceptible as a narrow canal. The epithelial cells 
lining it are short polyhedral, and show in the profile view very coarse thick rods, 
much more distinct than in any of the previous sections. Many cells appear possessed 
of short processes and more or less distinctly imbricated, a fact already known to Steu- 
dener. Each cell possesses a spherical or irregular or flattened nucleus situated near the 

lumen. 

In the human kidney the substance of the epithelial cells of this section includes 
occasionally a considerable amount of brownish pigment granules (Klein). 



STRUCTURE OF RENAL TUBULES. 259 

9. When entering the medullary ray in the cortex the ascending limb becomes nar- 
rower ; while ascending in the medullary ray it varies in thickness, in some places becom- 
ing again as thick as the preceding section of the boundary layer. 

The lumen is very small, and the epithelial cells are the more flattened the narrower 
the tube ; but they retain the flattened or angular nucleus next the lumen, and they also 
show the rods, but distinctly only in the outer part, i.e. next the membrana propria. Just 
like the cells of the previous section, they appear in many places very angular and 
possessed of processes, and imbricated. 

10. The irregular tubule is one of the most conspicuous sections ; it is situated 
amongst the convoluted tubules of all parts of the labyrinth, and has a very irregular and 
angular outline, in some places three and four times as thick as in others, and then of 
almost the same breadth as a convoluted tubule. But this greater thickness is due merely 
to a greater thickness of the lining epithelial cells, the lumen remaining everywhere a 
very narrow canal. The cells show in the profile-view exceedingly thick rods of a bright 
homogeneous aspect, more distinct than in any other section of the urinary tubule. 

The cells are very angular and in many places imbricated. But in this, as in the 
former cases, this imbrication is due to the irregular outline of the tube and the great 
variation in height of the adjacent cells. Each cell possesses an oval or angular nucleus 
next the lumen. 

1 1. The intercalated section of Schweigger-Seidel, or the distal convoluted tubule, is 
situated wherever the proximal convoluted tubule is found, with which it is identical in 
all respects. 

12 and 13. The curved part of the collecting tube and the next following straight 
section of the collecting tube, situated in the medullary ray, are thin tubes witli a distinct 
lumen, lined by a single layer of homogeneous cells, each with a spherical or oval nucleus. 
The shape of these cells varies greatly, some being polyhedral, others spindle-shaped 
and flattened, and still others angular and possessed of short processes. 

14. This section of the collecting tube belongs to the boundary layer ; it is broader 
than the preceding one, its lumen being larger and the lining epithelial cells more poly- 
hedral, although there are still some more or less flattened cells amongst them. Many 
of the cells are angular, being drawn out into short processes. Each cell possesses a 
homogeneous matrix, and in it a spherical or oval nucleus. In the human kidney the 
epithelial cells of this section of the collecting tube are short columnar, but otherwise 
similar to those described just now. 

With the exception of the descending limb of Henle's loop (5) and the loop itself (6), 
there appears in all other sections of the urinary tubules of the cortex and boundary 
layer of the kidney of the dog a delicate membrane lining the inner surface of the 

R R 



2 6o ATLAS OF HISTOLOGY. 

epithelium, that is next the lumen. From place to place an oblong nucleus can be 
seen in it more or less distinctly wedged in between the epithelial cells. In the convo- 
luted tubules (both sections) and in the spiral tubule (9) the number of nuclei of this 
centre-tubular membrane is very small, but in the ascending limb of Henle's loop, 
especially in sections 8 and 10 of diagram 1, and also in the collecting tubes of the 
cortex, their number is considerable. They appear also here situated in depressions 
of the epithelium, and owing to the lumen of the tube being very narrow, as in sections 
8, 9, 10 and 12, the former appears almost entirely occupied by the centrotubular mem- 
brane and its nuclei. 

15 and 16. The collecting tubes and ducts of the papillary portion possess a com- 
paratively large lumen lined with columnar transparent cells, each with an oval 
nucleus. The collecting tubes of the papillary portion join so as to form larger tubes ; 
the size of their lumen and the height of their lining epithelial cells are dependent on 
the size of the tube. 



The nuclei of all epithelial cells of the urinary tubules show a more or less dis- 
tinct intranuclear network within a limiting membrane. This network is best shown 
in the nuclei of the human kidney, and here again in those of the collecting tubes and 
ducts. 

Heidenhain, on the occasion of the discovery of the ' rod-structure 'of the substance 
of epithelial cells in the convoluted tubules (both sections) and in the ascending limb (of 
Henle's loop), both in the medulla and cortex of the mammalian kidney, made the im- 
portant observation that pigment matter (indigo-sulphate of sodium, phcenicin-sulphate 
of sodium) injected into the circulating blood of the dog and the rabbit is excreted by 
the epithelium of all those sections of the urinary tubules that possess the above-named 
rod-structure. Heidenhain maintains that the pigment is excreted through the substance 
of the epithelial cells themselves (rods and nucleus). Examining the kidney of the cat, 
into whose circulating blood carmine in ammonia had been injected, I find that carmine 
Granules are present in the interstitial substance between the epithelial cells of the same 
sections of the urinary tubules, as in the above cases of Heidenhain, but not in the 
substance of the cells themselves. This is quite in accordance with what has been 
shown as regards the excretion of pigment in other epithelial and endothelial structures, 
as mentioned on former pages in connection with the observations of Thoma, Arnold, 
Kuttner, and others (see p. 176), viz. that the pigment is deposited between and not in 
the epithelial or endothelial cells themselves. 



DISTRIBUTION OF BLOOD-VESSELS. 261 

The Blood-vessf.ls. 

These form distinct sets of vessels for the membrane of the pelvis, for the capsule, 
for the cortex, and finally for the medulla. Those of the pelvis and calices terminate as 
a network of capillaries underneath the epithelium. The arterial branches of the capsule 
are derived either from the extrarenal parts or from the cortical arteries, viz. from the 
interlobular branches. The efferent veins of the capsule are likewise of two kinds, viz. 
such as empty themselves into extrarenal veins and others leading into the stellate veins 
of the cortex. The former generally run in twos, in company with the arterial branches. 
The capillaries of the capsule are very numerous, and form a network with uniform 
meshes. 

The large trunks of the arteries and veins, both for the cortex and medulla, 
penetrate, as already mentioned, from the submucous tissue of the pelvis into the 
boundary between cortex and medulla, whence they send off or take up respectively the 
branches supplying the cortex and medulla. 

a) In the cortex. The arterial branches ascend from the first-named trunks in the 
middle of the sections of the labyrinth situated between two neighbouring medullary rays. 
These arterial branches are called the interlobular branches. While ascending towards 
the periphery of the cortex they give off from all sides of their circumference short vessels, 
the afferent arterioles, running transversely, one for each Malpighian corpuscle, where 
they break up into the network of capillaries forming the glomerulus described on a 
previous page. Some of the afferent arterioles before entering the Malpighian corpuscle 
give off a short lateral branchlet that breaks up into capillaries for the convoluted 
tubules. 

Many arterise interlobulares are exhausted when they reach the periphery of the 
cortex, that is the part that does not contain any Malpighian corpuscles ; but some 
penetrate into this layer, and terminate in the capillary blood-vessels, surrounding 
with their meshes the convoluted tubules ; and finally a small number pass even beyond 
this layer and penetrate into the outer capsule, as mentioned above. 

The efferent vessel of the Malpighian corpuscle is a venous vessel, and breaks up 
into a dense network of capillaries that entwine all tubes both of the labyrinth, including 
the peripheral layer, as well as of the medullary rays, the meshes of the former 
being more round, those of the latter elongated. In addition to the efferent vessel 
of the Malpighian corpuscles, the above-named branches of the afferent arterioles, and, for 
the peripheral layer of the cortex, the last outrunners of the interlobular arteries are 
to be named as supplying the capillaries of the cortex. The network of capillaries 
of the labyrinth and medullary rays forms one continuous system for the whole cortex. 

R R 2 



262 ATLAS OF HISTOLOGY. 

The venous branches are distributed in the labyrinth, in the following manner. 
The capillaries of the peripheral layer of the cortex, viz. that without Malpighian 
corpuscles, lead into minute venous rootlets which open into a vena stellata, called so 
from the manner of the arrangement of its rootlets. Each vena stellata passes 
into the labyrinth of the cortex, and accompanies the arteria interlobularis as the 
vena interlobularis. On its way it takes up transverse branches coming from the 
capillary network of the labyrinth. The vena? interlobulares lead into the venous 
trunks situated between the cortex and medulla. 

b) In the medulla. From the large arterial trunks situated between the cortex and 
boundary layer short branches are given off, which having entered the latter split up Into 
bundles of straight arterioles, the arteriolar rectse. 

The vessels belonging to one such bundle are all arterioles, and their number is 
increased by the addition of the vas efferens of the Malpighian corpuscles situated next 
the boundary layer. 

These arterioles run in the boundary layer between the bundles of urinary tubules 
which, as mentioned on a former page, are the continuations of the medullary rays. 
On their way towards the papilla their number gradually decreases as they pass laterally 
into a network of capillaries for the urinary tubules, the meshes of which are elongated. 
At the margin of the cortex and medulla the capillaries of the former are con- 
tinuous with those of the latter. 

The veins originate as single vessels, beginning at the papilla, and their number is 
gradually increased by vessels coming out from the capillary network of the urinary 
tubules. Just like the arteries, so also the veins form bundles, venae rectae ; these 
bundles are very considerable while running through the boundary layer between the 
continuations of the medullary rays. They empty themselves into the trunks 
situated between the cortex and medulla. The bundle of urinary tubules forming, 
in the boundary layer, the continuation of a medullary ray, has on one side a 
bundle of arterioe rectse, and on the other one of venae rectae ; and between them 
there is a network of capillary vessels with elongated meshes winding round the urinary 
tubules. 

Near the papilla the vessels form a uniform network with elongated meshes, and 
on the summit of the papilla itself we find around the mouth of each urinary duct 
a very delicate network of capillary veins. 

In the foregoing description of the blood-vessels, I have followed Ludwig in his 
article on the Kidney, in Strieker's 'Manual of Histology.' The diagram 3 of Plate 
XXXVI Ia., copied from Ludwig, gives a clear view of the distribution of the vessels 
in the cortex and medulla. 



DISTRIBUTION OF LYMPHATICS. 263 

Numerous lymphatics arranged in a plexus are present in the capsule of the kidney ; 
they may be traced into lymph spaces between the convoluted tubules of the periphery 
of the cortex (Ludwig). In the connective tissue accompanying the large blood-vessels 
may be seen a plexus of lymphatic vessels ; from these the injection matter passes freely 
into the lymphatics of the capsule and into the lymph spaces between the urinary tubules 
both of the cortex and medulla. 



The Ureter and Bladder. 



The ureter is lined with stratified transitional epithelium ; this consists of: a super- 
ficial layer of polyhedral cells of various sizes, each with one, two or more spherical or 
oval nuclei ; then follows a layer of club-shaped or pear-shaped columnar cells, each with 
a spherical or oval nucleus ; the broad part of the cells is directed towards the surface, the 
narrow stalk towards the depth; between these are wedged in other cells, spindle- 
shaped or conical cells, each with a flattened oval nucleus (see Chapter II.). The 
number of layers of these deep cells varies in different parts and according to the 
state of contraction of the ureter; it is greater in the contracted, smaller in the less 
contracted state. In the former state the epithelium as a whole is much thicker at the 
base than at the top of the folds. 

The mucosa underneath the epithelium is a connective-tissue membrane, contain- 
ing a dense network of blood capillaries in almost immediate contact with the epithelium 
(Engelmann). The loose submucous connective tissue is continued, as septa, between tin- 
muscle bundles of the next or muscle coat. This consists of bundles of unstriped 
muscle cells, which bundles form networks. They are grouped into an inner and outer 
longitudinal and a middle circular coat. Fibrous-connective tissue forms an outer thin 
sheath or adventitia. 

There are rich plexuses of non-medullated nerves in the muscular coat, which in 
all respects resemble the ground plexuses already mentioned of the unstriped muscular 
tissue. In the nerve branches of the adventitia Obersteiner, and also Dogiel, observed 
ganglion cells. 

The bladder is almost identical in structure with the ureter, with the difference that 
the mucosa, submucosa, muscular coat and adventitia (peritoneum) are much thicker. In 
the muscular coat the bundles run in a more irregular direction : in the greater part of 
the bladder those next the submucosa are more or less circular ; outside these are 
bundles running more obliquely ; and the outermost layer is composed of longitudinal 
bundles (Jurie). Towards the fundus the longitudinal bundles greatly prevail. 



264 ATLAS OF HISTOLOGY. 

In connection with the plexus of non-medullated nerve fibres of the serous and 
subserous connective tissue are numerous smaller and larger ganglia (Fr. Darwin) ; 
some of the nerve branches connected with them have an intimate relation to the large 
blood-vessels of these parts. 

In connection with the nerve branches of the muscular coat are also groups of 
ganglion cells ; they have been figured in Plate XXIII. and described on p. 120. 

According to Kisselew the nerve fibres of the mucosa terminate in special cells 
situated amongst the epithelial cells of the inner surface. 



PLATE XXXVIIa. 

Fig. I. is a diagram showing the course of the renal tubules and their variations 
in the different sections of the cortex and medulla. 

a. Cortex limited on its free surface by the capsule. 

a. Subscapsular layer not containing Malpighian corpuscles. 

a v Inner stratum of cortex without Malpighian corpuscles. 

h. Boundary layer. 

c. Papillary part next the boundary layer. 

1. Bowman's capsule of the Malpighian corpuscle. 

2. Its neck. 

3. Proximal convoluted tubule. 

4. Spiral tubule of Schachowa. 

5. Descending limb of Henle's loop. 

6. The loop proper. 

7. Thick part of the ascending limb. 

8. Spiral part of the same. 

9. The narrow ascending limb in the medullary ray. 

10. The irregular tubule. 

11. The intercalated section of Schweigger-Seidel, or the distal convoluted tubule. 

12. The curved collecting tubule. 

13. The straight collecting tubule of the medullary ray. 

14. The collecting tube of the boundary layer. 

15. The large collecting tube of the papillary part. 

In the papilla itself, not represented here, this tube becomes confluent with others 
and thus forms : 

16. The duct. 













•* %, 



^m 























1 -i i t i r T -* | f i i | t i i i ■ n 



_ ii i — Ti'ii" 



DISTRIBUTION OF RENAL TUBULES. 265 

Fig. II. Copied from Klein, fig. 149 in 'Handbook for the Physiol. Laborat.' 
Magnifying power about 350. 

From a section through the cortical substance of a human fcetal kidney. 
a. Glomerulus. 

c. Epithelium covering the glomerulus. 

d. Flattened epithelium lining Bowman's capsule. 
y. Urinary tubules in section. 

Fig. III. Copied from Ludwig, fig. 150 in Strieker's ( Manual of Histology.' 
Diagram of the vessels of the kidney. 
at. Interlobular artery. 
pi. Interlobular vein. 
g. Glomerulus of Malpighian corpuscle. 
vs. Vena stellata. 
ar. Arteria recta. 
vr. Vena recta. 
ab. Bundle of arteriolar rectae. 
vb. Bundle of venae rectae. 

vp. Network of vessels around the mouth of ducts. 

Fig. IV. Two fully developed spermatozoa, as seen under a high power. Copied 
from H. Gibbes, in ' Quarterly Journal of Micro. Sciences,' October, 1879. 

a. Of triton cristatus. 

b. Of horse. 

Fig. V. From a section through the ovary of a rabbit, prepared in chloride of gold, 
showing part of the epithelium lining a Grafian follicle, as viewed in profile. A very 
beautiful nucleated reticulum is seen stretching from the membrana propria to the zona 
pellucida of the ovum between the epithelial cells of the membrana granulosa. Mag 
nifying power about 350. 

PLATE XXXVIII. 

Fig. I. From a vertical section through the kidney of the dog, showing part of the 
labyrinth and the adjoining medullary ray. 

The capsule of the kidney is supposed to be on the right-hand side. Magnifying 

power about 350. 

a. The capillaries of the Malpighian corpuscle, viz. the glomerulus, are arranged in 
lobules. Bowman's capsule with its lining of flat epithelial cells, and the fiat epithelial 
cells covering the glomerulus, are well shown. 

The stalk of the glomerulus is directed to the left, and is cut away obliquely. 



266 ATLAS OF HISTOLOGY. 

n. Neck of the Malpighian corpuscle. 

c. Convoluted tubules cut in various directions. 

The rodlike structures in the substance of the polyhedral epithelial cells is well shown. 
b. The irregular tubule, 10 in diagram i of the preceding Plate. 

d. c. and /. belong to the medullary ray. 

d. Collecting tube (13). 

e. Spiral tube (4). 

/. Narrow section of the ascending limb (9). 

The nature of the lining epithelium and its differences in these various tubes is 
well marked ; see the text of this chapter. 

Fig. II. From a vertical section through the same kidney as in fig I., showing the 
tubes of Henle's loops at the point of transition from the papillary part into the 
boundary layer. Magnifying power about 300. 

a. The first thick part of the ascending limb (7 of diagram 1 of the preceding Plate) 
at the point of demarcation of the papillary part and the boundary layer. 

b. and c. The transparent thin tubules of Henle's loops. 

Fig. III. From a vertical section through the cortex and boundary layer of the kidney 
of the dog; showing the blood-vessels injected with Berlin blue. Low magnifying power. 

a. Peripheral subscapsular part of the cortex. 

b. Cortex, showing the glomeruli of Malpighian corpuscles, the dense network 
of capillaries of the labyrinth and of the medullary rays. The thin branches of the 
laro-e vessels are the interlobular arteries, the thick ones the interlobular veins. 

c. Boundary layer showing the bundles of arteriolar rectae and venae rectse ; see 
diagram 3 of preceding Plate ; between these bundles are seen the capillaries, forming a 
network with elongated meshes around the urinary tubules. 

Fio-. IV. From a horizontal section through the cortex of the human kidney, show- 
ino- the honey-combed transparent matrix in which the urinary tubules and the capillary 
blood-vessels are embedded ; a few branched nucleated connective cells are seen in it. 

The large cavities correspond each to a transverse section of a urinary tubule, 
whose epithelium, except in one tube, has been removed by accident. The two small 
holes, at the side of the tubule whose epithelium is still present, are transverse sections 
of capillary blood-vessels. Magnifying power about 400. 

Fig. V. From a vertical section through the same kidney as in fig. I. Magnifying 
power about 300. 

a. Capsule of the kidney. 

b. Convoluted tubules cut in different directions. 

c. Irregular tubule (10). 



STRUCTURE OF RENAL TUBULES, 267 

d. Curved part of the collecting tube (12). 

Fig. VI. From a horizontal section through the papillary portion of the human 
kidney. Magnifying power about 300. 

In a uniformly stained transparent ground substance, which in reality is composed 
of fibrous connective-tissue, are seen urinary tubes and blood-vessels cut transversely. 

a. Large collecting tubes. 

b. Smaller ones. 

c. Tubes of Henle's loops. 

d. Capillary blood-vessels. 

e. Venous capillaries ; the endothelium is accidently detached from the wall of the 
vessels. 

Fig. VII. From a vertical section through the same kidney as in fig. I., showing 
under a very low power the adjoining portions of the cortex and the boundary layer. 

a. Labyrinth containing Malpighian corpuscles and convoluted tubules cut in various 
directions. 

b. Bundles of urinary tubules of the boundary layer continued into the cortex as 
the medullary rays. 

c. Bundles of blood-vessels, arterise or venae rectae. 

Fig. VIII. From a vertical section through the labyrinth of the kidney of the cat, 
into whose circulating blood carminate of ammonia had been injected. 

a. Convoluted tubules cut transversely. 

b. Part of a spiral tubule of the medullary ray. 

Between the tubules are capillary blood-vessels, injected with Berlin blue. The 
carmine is deposited, that is, has been excreted, not in the substance of the epithelial 
cells, but in the cement substance between them. When seen from the surface, the 
outlines of the epithelial cells are marked as a beautiful pink mosaic. Magnifying 
power about 350. 

Fig. IX. From a vertical section through the cortex of the human kidney as seen 

under a very low power. 

a. Capsule. 

b. Urinary tubules cut in various directions. 

c. Medullary rays and between them the labyrinth of tubules with Malpighian 

corpuscles. 

The medullary rays are lost at some distance from the capsule ; see the text of this 

chapter. 

Owing to the very low power structural distinctions of the urinary tubules cannot 

be recognised. 

s s 



268 ATLAS OF HISTOLOGY. 



CHAPTER XXXI. 

THE MALE GENITAL ORGANS. 

Testis and Epididymis of Man and Mammals. 

Tim. framework. — The capsule of the testis consists of an external and internal fibrous coat. 

The external coat, the tunica adnata, or the visceral layer of the tunica vaginalis propria, 

is a serous membrane, and consequently is a dense connective-tissue feltwork, with 

numerous elastic fibrils connected into a network. It is supplied with a network of 

capillaries and numerous nerve fibrils arranged in a plexus. On its outer or free surface it 

is covered with a single layer of flattened endothelial plates. Minute villi projecting 

from the surface contain, according to the state of development, a greater or smaller 

amount of connective-tissue ; they are continuous with the ground membrane and are 

covered with germinating endothelial cells (see Chapter III.). The internal coat, or the 

tunica albuginea, is of lamellar structure, the lamellae being composed of bundles of 

fibrous connective-tissue with the corresponding flattened connective-tissue cells. Its 

thickness increases towards the posterior margin of the testis, in which place, in the 

human organ, there exists a considerable accumulation of it, as the corpus Highmori, 

or the mediastinum testis. 

As shown by Messing, the testis of the dog, cat, bull, pig, sheep, rabbit, hare, guinea pig, &c, 
possesses a central corpus Highmori ; that of the mole, hedgehog, and bat a peripheral one ; the 
rat and mouse have no corpus Highmori. 

Numerous septa extend from the sides and front between the albuginea and the corpus 
Highmori ; these septa are of the same structure as the albuginea and the corpus 
Highmori. Unstriped muscular fibres are mentioned by Kolliker as present in them. 
A dense plexus of lymphatics, being the efferent vessels, is contained in the capsule of 
the testis, most vessels being situated between the outer and inner coat. The inner coat 
possesses also a rich network of blood-vessels. 

The connective-tissue septa are continuous with the connective-tissue existing 
between the seminal tubules, and are the carriers of the blood-vessels. The intertubular 
or interstitial connective-tissue, which has been carefully studied by Mihalkovics, in the 
confirmation of whose observations I join Gerster, has a conspicuously lamellar structure ; 
each lamella consists of: (a) an endothelial membrane, that is, a hyaline membrane 



CONNECTIVE-TISSUE OF TESTIS. 269 

composed of endotheloid plates (connective-tissue corpuscles), each with a clear, oval 
flattened nucleus ; and (b) a small amount ot" fibrous connective-tissue, arranged as a 
plexus of fine bundles, or fenestrated membrane. The endothelial membrane covering 
this plexus is not a continuous membrane, but perforated by numerous holes which, 
coincidino- with the fenestrations of the plexus of fibre bundles, forms the means of 
communication between neighbouring interlamellar spaces. These spaces are lymph 
spaces, and they are the rootlets of the lymphatic system of the testis (Ludwig and 
Tomsa), the above-mentioned endothelial membrane being a one-sided endothelial lining 
of the spaces ; its presence has been known to Frey, Tommasi, Kolliker, v. La Valette 
St. George, and others. 

The number of lamellae present between the seminal tubes varies greatly in the 
testis of different animals, and in different parts of the same testis; in some animals 
(cat, doo-) it is very considerable, in others only indicated (rat, mouse). The relation 
between the lamellae and the seminal tubes is a very intimate one, but depends in a 
great measure on the amount and distribution of the fluid present in the interlamellar 
lymph spaces. For it. is clear that if the interlamellar spaces, midway between two con- 
tiguous tubules, be distended, while those next the tubes are collapsed, the appearance 
will be produced as if the lamellae next the tubes were part of the limiting membrane of 
the latter (Henle, Frey, Hessling, Kolliker, and others) ; but their separate and inde- 
pendent nature is easily recognised in places where the interlamellar spaces next the 
membrana propria of the seminal tubes are distended. It is then ascertained that the 
former, viz. the membrana propria, is a single homogeneous membrane, separated by a 
lymph space from the lamella next to it. The oval nuclei, present in the membrana 
propria (see below), are not to be confounded with those of the endothelial cells outside. 
In the rat there exists only a very small amount of this intcrtubular connective tissue, and in 
many parts the seminal tubules are separated from each other by an open lymph space ; in this 
case the membrana propria is covered with a continuous layer of beautiful endothelial plates. 

Between the lamellae of the intertubular connective-tissue are found groups of 
peculiar cells, arranged as longer or shorter, thicker or thinner, cylindrical, plate-like, or 
irregularly shaped, anastomosing masses. They are known since Kolliker, and have 
been considered by this observer as indifferent cells of the connective-tissue. Sub- 
sequent observers, especially Henle and Leydig, gave their attention to these cells; 
Waldeyer and Mihalkovics regard them in the same light, and consider them as the 
interstitial or parenchymatous connective-tissue cells. R. Harvey thinks these cells are 
ganglion cells. I have described them as epithelial cells, being derived from the 
epithelial columns of the Wolffian body, and corresponding to similar cells found in the 
ovary (see below). I consider them as intertubular, or interstitial, epithelial cells. 



s s 2 



2?Q ATLAS OF HISTOLOGY. 

These cells are polyhedral, each with a spherical nucleus situated in the centre (cat 
and dog), or excentrically (guinea pig, boar). The cell substance appears ' granular/ 
but is in reality an exceedingly beautiful and dense network. In some instances (guinea 
pig) there are brownish-yellowish pigment granules contained in the cell substance. 
The nucleus includes within a distinct membrane a pale, honey-combed reticulum, 
containing occasionally one, seldom more, thickenings, nucleoli. The intranuclear and 
intracellular reticulum form a direct continuity. 

As mentioned above, the groups of intertubular epithelial cells are situated between 
the lamellae. Their number varies in different animals. They are most abundant in the 
dog, cat, and especially boar, where they form a predominant portion of the whole testis 
(Leydig). In this last instance the masses of these intertubular epithelial cells are sup- 
plied with their special system of blood-vessels. 



The parenchyma consists of the seminal tubes, arranged in the well-known lobules 
between the above connective-tissue septa. The tubes are relatively large and very wavy 
and much convoluted ; they possess a few lateral branches, by which they become 
connected into a network ; they form terminal loops ; in the peripheral portion of the testis 
the tubules are possessed of minute lateral caecal branchlets (Mihalkovics). These 
branchlets are especially well shown in the young state (v. la Valette St. George). 

Each seminal tubule in the adult testis is limited by a membrana propria, which 
appears as a hyaline elastic membrane, and containing oval, flattened nuclei at regular 
intervals, is probably an endothelial membrane. It is supported on its outside by 
the lamellae of the intertubular tissue. Inside this membrana propria are several 
layers of epithelial cells, the seminal cells. Of these may be distinguished the outer, and 
the inner layer of cells. The former are situated next to the membrana propria. They 
are more or less polyhedral in shape, of about the same size, and possess faint outlines. 
They correspond to the germ-cells of Sertoli ; their substance is transparent, and appears 
uniformly and finely granular, which appearance is due to the presence of a delicate 
reticulum. Each of these cells possesses a nucleus, and in this respect, and in this 
respect only, the cells are of two very distinct types (Klein) : (a) such as contain an 
oval, transparent nucleus, limited by a definite membrane, and containing a more or less 
well-developed, honey-combed reticulum, with generally one, and occasionally two, or 
even three, irregularly shaped thickenings, or nucleoli ; (b) the cells of the second type 
include each a spherical nucleus ; this is slightly smaller than that of the former cells, 
it has no definite limiting membrane, and contains in a transparent matrix a beautiful 
convolution of relatively thick and short filaments, or rods, twisted in many directions, 



STRUCTURE OF SEMINAL CELLS 271 

and anastomosing with one another by relatively few lateral branchlets. These fibrils, or 
rods, stain very well in dyes, and, when looked at under a low power, present them- 
selves as spherical, or more or less elongated, isolated dots, that is, according to 
whether they are viewed in optical transverse, oblique, or longitudinal section ; but, 
under a high power and on careful focussing, it is soon ascertained that they are in 
reality fibrils or rods arranged in more or less complex convolutions. 

Next to this outer layer of cells, but nearer to the lumen, are the inner seminal eeils 
(celluli seminales of Sertoli) ; only in few tubes are these cells limited to one or two 
layers, generally they are arranged in more than two layers. These inner cells are 
polyhedral where they are situated closely side by side, but more spherical next the 
lumen of the tube, because more loosely connected with one another ; they are of about 
the same size, and composed of a transparent substance with faint outlines, and include 
a single nucleus ; this is identical with the nucleus of the above second type, viz. it is 
spherical, does not possess any limiting membrane, and contains a beautiful convolution 
of thick fibrils or rods in a transparent matrix. Whether the cells lie closely side by 
side, as is the case with those of the outer layer and those immediately next to it, 
or not, as those near the lumen of the seminal tube, they are always separated by a 
transparent interstitial substance ; in the former case there is only a trace of it. A 
nucleated reticulum, in the meshes of which the seminal cells are contained, is found in 
some places to occupy that interstitial substance. This reticulum, first discovered by 
Sertoli, and called germ-reticulum by v. Ebner, supporting cells by Mcrkel, is not 
accepted by Mihalkovics ; but there can be no doubt about its existence in the seminal 
tubes (Afanassiew). Its significance is probably no other than that of a similar reticulum, 
mentioned in former chapters in connection with various other glands, viz. it is continuous 
with the membrana propria and forms a support for the lining epithelial cells. 

Now, when examining more carefully the fibrils of the nuclei of the second type 
of the outer cells, and those of the nuclei of the inner cells, it will be found that 
their arrangement is subject to certain definite variations: (1) either the fibrils form 
a uniform convolution, that is, they are distributed uniformly throughout the nucleus, 
being more or less twisted and united into a network ; or (2) the fibrils are arranged 
in the periphery, but transversely in one and the same direction ; a nucleus of this sort, 
when viewed in the direction of the fibrils, appears as if transversely ribbed, but viewed 
vertical to it, as if dotted at the periphery ; or (3) the fibrils radiate towards one or two 
centres. All these differences indicate changes preparatory to division, as is now well 
known from the works of Strassburger, Hertwig, Mayzel, Eberth, Balfour, Schleicher, 
Peremeschko, and especially Flemming, whose very extensive and beautiful observations 
on the chancres of the nucleus during division have been found fully confirmed by myself 



ATLAS OF HISTOLOGY. 

2 1 - 

in the case of the epithelial cells of the newt. As will be minutely considered in a 
future chapter, the above forms correspond to what is termed (Flemming, Klein) : the 
' convolution/ the ' basket/ the < wreath/ the ' monaster/ or the ' dyaster/ 

The oval nucleus, with the transparent, honey-combed reticulum, viz. the nucleus of 
the first type of the outer seminal cells, corresponds to a ' resting nucleus ' (Flemming), 
that is, a nucleus not in the state of division. The number of these ' resting nuclei ' is 
subject to considerable variations in different tubes ; while in some they are relatively 
few and limited only to the outer layer of cells, we find, in others, their number much 
greater, and not limited only to the outer layer of cells, but present also, though very 
rarely, amongst the cells of the inner layers. 

Towards the lumen of the tube the cells, as already mentioned, are loosely connected, 
and, in some places, their nucleus is seen in the very state of dividing, or already divided, 
into two small daughter nuclei, each with fibrils and rods of a similar arrangement as 
before the division (see a future chapter). In the latter instance the cell itself is just 
dividing, or has already divided, into two small daughter cells, each with one daughter 
nucleus. The cell substance of these daughter cells is less transparent than that of the 
mother cell, and its outline is very well marked. 

The mother nucleus, as well as the daughter nuclei, during division, or immediately after, shows, 
as a rule, very clearly, in well prepared and stained sections, the above-mentioned arrangement of 
the fibrils or rods, but in some places the latter (fibrils or rods) are not distinct, the nucleus or 
nuclei appearing as a more or less uniform knobbed single or double clump, staining deeply in 
dyes. 

In some tubes the number of the (small) daughter cells is greater than in others ; in the 
former they may be found arranged in several layers loosely connected with one another. 

Amongst the seminal epithelial cells with one nucleus are found, especially in the cat 
and dog, occasionally, but on the whole not frequently, large multinuclear cells. Where 
they occur they are found in groups, but the individual cells are more or less separated 
from one another. They are of very various sizes ; some have a limited number of nuclei 
(2-4), others have 8-12 or more. The cells are spherical, and each of the nuclei 
contained in them is spherical, and of precisely the same nature as those of the 
inner seminal epithelial cells, viz. without a definite membrane and containing filaments 
or rods arranged in a complex manner, preparatory to division. 

In few instances of the testicle of the cat are found, besides the multinuclear cells 
just mentioned, other large cells with one or several homogeneous nuclei deeply staining 
in logwood ; these nuclei appear irregularly shaped, lobed, or possessed of knob-like 
prominences. 

Now, the small cells, mentioned above as the daughter cells, undergo very interesting 



CHANGES OF SPERMATOBLASTS. 273 

changes, leading to the formation of the spermatozoa ; for this reason they may be 
called the spermatoblasts (Sertoli). In describing these changes I shall refer to observa- 
tions on the testis of man and various mammals (rabbit, mouse, guinea pig, dog, cat, 
and boar), which, although not completed yet, nevertheless permit already of a general 
statement of the plan of the formation of the spermatozoa. 

Starting with the above-mentioned daughter cells or spermatoblasts, each with one small 
nucleus and arranged loosely next the lumen of the tube, we find that soon after their 
formation, their nucleus, while retaining its spherical shape, alters in so far as it becomes 
invested in a distinct membrane, and its convolution of fibrils or rods changes into a 
transparent honey-combed reticulum, in many instances without, but in some with one or 
two thickenings, nucleoli ; that is to say, the nucleus becomes similar to what has been 
mentioned on the previous page as a ' resting,' i.e. non-dividing nucleus. At the same 
time we notice that the nucleus is not placed in the centre, but in the periphery of the cell. 

Next, the nucleus becomes uniform in its substance, and transparent; it stains less in 
dyes, and all traces of a reticulum disappear. The cell substance is collected at one end 
of the nucleus as an elliptical granular mass, and appears separated from it by a trans- 
parent, clear bag. 

In the next stage the nucleus becomes flattened and discoid, so that when viewed 
from the surface it is broad and circular, but appears narrow and stafT-shapcd when seen in 
profile. The cell substance at this time is drawn out into a cylindrical or club-shaped 
granular body separated from the nucleus by a shorter or longer clear lube, the former 
clear bag. At the front part of the nucleus is seen a short and tapering curved 
projection, and at its hind end— viz. that directed towards the clear tube and cell 
substance — there is also to be found a short pointed process extending into the clear tube 
just named. When examining one of these cells in a well stained specimen under a high 
magnifying power, it is seen that the hind third of the nucleus is tightly grasped by 
the front end of the above clear hebe, and that the granular body — viz. the remnant 
of the cell substance — is placed like a cap over the hind end of the clear tube. 

In the next stage the nucleus becomes more flattened and oblong, and in some 
animals more or less curved, while both the clear tube and the granular body become 
elongated. It is not easy to ascertain whether the clear tube extends also over the 
front part of the head. In the last stage the granular body has become changed into 
a long, thin, and homogeneous filament. 

The fully developed and ripe spermatozoon consists of a homogeneous, well-defined, 
discoid oval head, which in some animals is in the profile view more saucer-shaped — i.e. 
convex concave — than in others ; it possesses a more or less distinct, tapering, minute 
curved prolongation. Next to the head is the middle piece of Schweigger Seidel ; its 



274 ATLAS OF HISTOLOGY. 

length differs in different animals ; it appears homogeneous and rod-shaped ; attached 
to it is the filament, or tail, thinner and much longer than the middle piece, and ending 
in a pointed extremity. In triton and salamander the filament, or tail, is continued over 
the middle piece as a very conspicuous, wavy, or more or less spiral filament, but is sepa- 
rated from it (middle piece) by a thin homogeneous membrane (Leydig, Gibbes). This 
filament appears fixed to the blunt hind end of the head ; this latter contains here an 
oval bright corpuscle, and is a very long and slightly curved rod, ending in front in a 
pointed extremity. 

It is probable, from the observations of H. Gibbes : (a) that a similar arrangement 
exists also in man and mammals, viz. that the filament is continued over the middle 
piece as a fine wavy or spiral thread ; but here this thread lies close on the former, viz. 
the middle piece ; and (6) that there is a sheath which covers the hind part of the head, 
and continued over the middle piece. 

In what relation do, then, these different parts of the fully formed spermatozoon 
stand to the parts of the developing element, that is, the spermatoblast ? A comparison 
shows at once that the head of the ripe spermatozoon is the changed nucleus of the 
spermatoblast ; that the filament, or tail, is derived from what has been mentioned above 
as the granular body of the original cell. The middle piece of Schweigger Seidel 
is an outgrowth of the nucleus of the spermatoblast, that is, of the head of the sperma- 
tozoon, and the clear tube of the developing spermatozoon, described above as embrac- 
ing the hind part of the nucleus and separating the latter from the granular body, is the 
sheath which in some instances (triton and salamander) is observable on the middle 
piece of the fully-formed spermatozoon. 

The preceding statements very well agree with the observations of Kolliker, Henle, 
Schweigger Seidel, of v. la Valette St. George, as described in his exhaustive article on 
this subject in Strieker's 'Manual of Histology,' and in other subsequent publications, 
and of the important researches both of Merkel and Sertoli, which are to the effect that 
in mammalian animals, at any rate, the head of the spermatozoon is the transformed 
nucleus, while the filament, or tail, is derived from the body of the spermatoblast. 



While the spermatoblasts or the daughter cells of the inner seminal cells undergo the 
changes which lead to their conversion into spermatozoa, important alterations occur in 
their position and arrangement. As described on a former page, the spermatoblasts lie 
more or less loosely side by side next the lumen of the seminal tube, their number varying 
greatly in different parts. Now, as soon as the stage is reached when the nucleus is 
flattened, and, as it were, free of the cell body, and this latter converted into a club- 



DEVELOPMENT OF SPERMATOZOA. 275 

shaped, granular mass, separated from the former by a clear sac or tube, these so altered 
spermatoblasts, which we shall henceforth designate as the 'young spermatozoa,' assume 
a definite arrangement, becoming collected into more or less conical, pyramidal, or fan- 
shaped groups, the stalk of which is sunk in between the inner seminal epithelial cells 
(see figs. VI.-VIII. of Plate XXXIX.). The young spermatozoa in each group are 
so placed that their nucleus, or head, is directed outwards, that is, towards the seminal 
epithelium, their granular bodies looking- in the opposite direction, that is, towards the 
lumen. As the spermatozoa elongate, the above groups also elongate, and their 
stalk becomes much thinner ; this latter contains now only the nucleus of the sper- 
matozoa (see figs. VII. and VIII. of Plate XXXIX.). The stalk remains sunk in 
between the seminal epithelial cells. It is impossible to say what causes this peculiar 
arrangement of the developing spermatozoa in groups, or how they are fixed in 
between the seminal cells. The young spermatozoa in each group are held together by 
a transparent, sometimes indistinctly granular interstitial substance. 

The inner broad ends of these groups, viz. next to the lumen of the seminal 
tube, are in the last-named stages close to one another, and connected into a network 
by a transparent, finely granular interstitial substance. This latter arrangement, viz. 
into a network, is of course shown only when these groups are viewed from the surface. 
Sooner or later, both the interstitial substance between the groups, as well as that be- 
tween the individual spermatozoa, breaks up, and the spermatozoa, having reached their 
full development, become detached from one another. 

The condition in which the seminal tubes, or the different sections of the same 
tube, present themselves, is, then, one of the following: (1) between the membrana 
propria and the lumen of the tube we meet with (a) the outer seminal cells, (b) the 
inner seminal cells, these latter in two or more layers, but in various stages, preparatory 
to division ; then follow (c) the daughter cells, or spermatoblasts, in one or more 
layers, but loosely connected. Or, (2) a and b are the same, but the spermatoblasts 
begin to change into young spermatozoa. Or, (3) a and b as before ; c, contains 
distinct young spermatozoa grouped in a definite manner ; these groups are short and 
thick. Or, (4) a and b as before ; c t the young spermatozoa are more developed and 
longer, their groups are more pyramidal, and each with a thin stalk sunk in between 
the inner seminal cells ; the free or broad ends of the groups are connected into a net- 
work by an interstitial substance. Finally, (5) a and b as before; c, the groups of 
young spermatozoa are disintegrating, the fully-formed spermatozoa becoming isolated. 
In the latter or even the previous condition we may find the inner seminal cells under- 
going again division into daughter cells. 

The formation of the spermatozoa is not fixed to any definite locality, nor does it 

T T 



2;6 ATLAS OF HISTOLOGY. 

occur or proceed with any regularity, for we may find any two of the above conditions 
not only in adjacent seminal tubes, but also side by side in the same tube. 

Some observers (v. Ebner, Neumann, Mihalkovics, and others) consider each of the 
above groups of spermatozoa as formed in a single large cell (spermatoblast of v. Ebner 
and Neumann), consisting of: a nucleated (v. Ebner) or non-nucleated (Neumann) 
basis at or near the membrana propria of the seminal tube : a thin prolongation (our 
peduncle) : and, finally, a broad fanlike lobed mass next the lumen of the tube, in which 
mass the spermatozoa are produced. 

Such a view, if correct, would completely upset the account given of the formation 
of the spermatozoa in the preceding pages. The view that each of our groups of young 
spermatozoa is at first a single large cell, in which spermatozoa are developed, rests 
chiefly on the assumption that the part we called the peduncle of the group is connected 
with one definite seminal epithelial cell, being, in fact, an outgrowth of it, an assumption 
which appears to me not verified by observation. On the other hand, the formation 
of the young spermatozoa can be traced distinctly from our spermatoblasts, or daughter 
cells of the seminal epithelium, as well as the gradual arrangement of the former (sperma- 
tozoa) into groups. 



The seminal tubules, when approaching the corpus Highmori, empty themselves 
into the vasa recta, which, in the corpus Highmori, by anastomosis become connected 
into the rete testis Halleri. The vasa recta and the tubes of the rete testis are much 
thinner than the seminal tubules ; there is a constriction at the passage of the convoluted 
seminal tubule into a vas rectum of men (Stieda). The vasa recta and the tubes of 
the rete testis possess a hyaline membrana propria lined with a single layer of transparent 
short columnar cells (Stieda), which in the guinea pig are squamous (Messing). 

The tubes of the coni vasculosi and the rest of the canal of the epididymis, including 
the vas aberrans Halleri, are considerably larger than the canals of the rete testis ; 
they possess a large lumen lined with columnar epithelium. Outside this epithelium 
is the membrana propria, supported and thickened by unstriped muscle cells, arranged 
chiefly as a circular coat, but some have also a longitudinal direction. 

The epithelium is composed of columnar thin cells, each with a bundle of exceedingly 
long cilia on the free surface (O. Becker, Kolliker). Each cell contains an oval nucleus 
in its outer portion. The substance of the cells is a beautiful reticulum, arranged pre- 
eminently in a longitudinal manner, and the cilia are prolongations of the fibrils of that 
network. The nucleus contains within a membrane the intranuclear reticulum. Under- 
neath the superficial columnar cells there is always a more or less distinct layer of small 



STRUCTURE OF EPIDIDYMIS, 277 

polyhedral cells. In some instances, amongst the superficial columnar cells, may be 
found goblet cells with or without mucous secretion. The cells, and their cilia, increase 
towards the canal of the epididymis. 

The thickness of the epithelium is greatly dependent on the state of contraction of 
the muscular coat ; it is, of course, greater when this (muscular coat) is contracted than 
when not. 

The seminal tubules, as well as the tubes of the epididymis, are surrounded by a 
rich network of capillary blood-vessels. 

Of the termination of the nerves in the seminal tubules and in those of the epidi- 
dymis nothing positive is known. 

In connection with the rete testis, Roth occasionally observed straight tubes, vasa aberrantia, 
running for a considerable distance along the epididymis, and terminating in a caecal extremity, 
simple or branched ; they are lined with a simple columnar ciliated epithelium. 

The tubes known as Giralde^s organ, and situated in the first part of the funiculus spcrmaticus, 
are lined with columnar epithelium, possessed of cilia (Roth). 

The pedunculated hydatid of Morgagni, situated on the head of the epididymis, which, 
since Luschka, Becker, and others, has been considered as the remains of the foetal Midler's duct, 
is covered with columnar ciliated epithelium (Fleischl). That its pyriform body is comparable 
to an ovary and the small canal attached to it to an oviduct, as maintained by Fleischl, has been 
disproved by Roth; Waldeyer compares the whole organ to the pars infundibuliformis of the 
oviduct. 



Vas Deferens and Vesicul/E Seminales. 

The vas deferens consists of a mucous membrane, a muscular coat, and an outer coat 
or adventitia. 

The mucous membrane is a dense connective-tissue feltwork, with networks of fine 
elastic fibres ; in it is found a rich network of capillary blood-vessels. 

The epithelium lining the canal is composed of columnar cells, which, with the 
exception of the part next the epididymis, are without cilia. Each cell includes an 
oval nucleus, situated in its outer part. The substance of the cell and nucleus differs in 
no way in structure from that described of columnar epithelial cells on several previous 
occasions. Between and underneath the columnar cells of this superficial layer are found 
conical, spindle-shaped, or polyhedral cells ; in the contracted state of the muscle coat 
these cells appear to be arranged in several layers, so that the epithelium looks much 
stratified. In the intraperitoneal portion the epithelium as a whole is generally thinner 
than in the rest of the vas deferens. 

The mucous membrane is much folded in the ampulla, and the minute depressions 

TT2 



27 8 ATLAS OF HISTOLOGY. 

of the surface hereby produced imitate glandular pits; they are considered as real 
glands by some observers (Henle, Leydig, and others). 

The muscular coat consists of an inner circular and an outer longitudinal stratum of 
unstriped muscle cells. At the commencement of the vas deferens there is, however, in 
addition, a thin inner longitudinal coat. 

The adventitia is fibrous connective-tissue, it contains the longitudinal bundles of 
unstriped muscle cells known as cremaster internus of Henle ; further, the rich plexus of 
veins known as plexus pampiniformis ; the plexus of lymphatic trunks with valves; and 
the nerve trunks of the plexus spermaticus. Small groups of ganglion cells and large 
ganglionic swellings are met with in connection with the branches of this plexus. 

In the vesicnlce seminales we meet with the same coats as in the vas deferens, but 
they are thinner in the former than in the latter. The mucous membrane is placed in 
numerous folds, whereby pits and grooves are produced resembling minute glandular 
depressions (Henle). The epithelium is composed of a superficial layer of long columnar 
cells and a deep layer of more or less polyhedral cells. 

The muscular coat is, as a whole, thinner than in the vas deferens, and consists of an 
inner and outer longitudinal and a middle circular coat of unstriped muscle cells, the 
first being the thickest. 

In the thick fibrous connective-tissue adventitia are the large blood and lymphatic 
vessels and the nerve trunks, with numerous ganglionic swellings, some of them of a 
considerable size. 

In the ductus ejaculatorii we also meet with a layer of columnar epithelial cells, and 
underneath these small polyhedral cells ; outside the epithelium is a delicate connective- 
tissue mucosa ; further outside is a muscular coat composed of an inner thick- 
longitudinal and an outer thinner circular layer. When passing into the vesicula 
prostatica the columnar epithelium is gradually replaced by stratified pavement 
epithelium. 

The Prostate Gland. 

The framework of the prostate gland is composed of a small amount of fibrous 
connective-tissue and of a great quantity of unstriped muscular tissue, The first forms 
the outer capsule and the thin septa passing inwards and carrying the blood-vessels ; 
the second is arranged as a network of septa and trabecular surrounding the different 
parts of the gland tissue proper. 

This latter consists of the ducts opening on the surface of the pars prostatica of the 
urethra, mostly at the basis of and near the colliculus seminalis ; they branch into 
smaller ductlets which pass into the gland-alveoli. These latter are longer or shorter, 
wavy or convoluted, branched tubes, terminating in saccular blind extremities ; many of 



STRUCTURE OF THE PROSTATE GLAND. 279 

them are possessed of short, lateral, club-shaped branchlets. On the whole, each 
duct, and its corresponding section of the gland tissue, are comparable to a compound 
tubular gland, as described in former chapters. 

The alveoli, as well as the ducts, possess a membrana propria, and a distinct lumen 
lined with epithelium. With regard to this latter the alveoli are of two different kinds : 
(1) alveoli lined with a single layer of thin and long columnar cells, each with an oval 
nucleus in the outer part of the cell ; (2) alveoli whose lumen is lined with a layer 
of short columnar cells, and outside this but inside the membrana propria there is another 
layer of small, cubical, polyhedral or spindle-shaped cells. The columnar cells of the 
former layer possess a thin process, which passes through the outer layer, and reaches the 
membrana propria. The stratified pavement epithelium^ of the urethra is continued a 
short way into the mouth of the ducts. 

The columnar cells lining the lumen of the alveoli, in the prostate gland of the 
newborn child, are much shorter than after puberty (Langerhans). 

The ducts are lined with a layer of columnar cells, underneath which is a layer of 
small polyhedral cells, each with a spherical nucleus. 

As in other glands, so also here the alveoli are surrounded by a dense network of 
capillary blood-vessels. Numerous ganglia are interposed in the plexus of the nerve- 
branches, present in the peripheral portion of the gland. In this portion occur also 
Pacinian corpuscles. 

The Urethra. 

The epithelium lining the mucous membrane is stratified pavement epithelium in 
the lower half of the pars prostatica and membranacea ; in the upper half it is stratified 
transitional epithelium ; in front of the bulbus urethras the epithelium becomes columnar 
first at the sides, latest in the lower part, There exist, however, in this respect great 
differences in different urethrae, and at different periods of life. Thus, in the newborn 
child, there are, amongst the columnar epithelium, islands of stratified pavement epithe- 
lium even in the pars cavernosa of the urethra. 

The fossa navicularis is lined with stratified pavement epithelium. Wherever this 
latter is found the mucous membrane forms minute conical papillae, containing loops of 
the superficial capillary network. 

The mucous membrane consists chiefly of fibrous connective-tissue, but there are 
present also large numbers of elastic fibres (Robin and Cadiat). It is surrounded by 
muscular tissue ; at the root of the urethra this is made up of an inner circular and 
an outer longitudinal layer of bundles of unstriped muscle cells ; in the pars prostatica 
the muscular coat is chiefly longitudinal and is intimately connected with the muscular 



28 ° ATLAS OF HISTOLOGY. 

tissue of the prostate; in the membranous portion of the urethra the muscular coat is 
also pre-eminently longitudinal, and its bundles pass into the mucous membrane itself, 
where they run in a longitudinal direction between the large venous vessels connected 
here into a network. These large veins empty themselves into smaller veins situated 
in the tissue outside the muscular coat. 

The plexus of large veins of the mucous membrane, with its muscular bundles just 
mentioned, represents the rudiment of a corpus cavernosum (Henle). 

In the pars cavernosa the muscular bundles are separated from one another by 
the venous sinuses or cavernae, and they form an essential part of the cavernous tissue 

Bes.des the lacunae Morgagni, the mucous membrane possesses small simple mucous 
gland tubes Imed with columnar epithelium (follicules of Robin and Cadiat) and 
longer branched mucous gland tubes, Littres glands. The epithelium of the surface 
penetrates into the mouth of their ducts. 

Each gland of Cow P er resembles in structure the sublingual gland, being a l arge com- 
pound tubular mucous gland (see Chapter XXV.). The chief duct possesses a thick 
coat, rich in longitudinal bundles of unstriped muscle cells. Its epithelium, as well as 
that of the large and small branches, is composed of columnar cells, longer in the 
arger branches than in the smaller one, In the gland tubes proper, or alveoli, the 
lumen is relatively large, and lined with columnar 'mucous' cells, whose outer thin 
portions are imbricated (Langerhans) in the same way as those described of the sub- 
maxillary gland of dog (see Chapter XXIV.). The substance of the cells is a beautiful 
reticulum (Langerhans) ; the nucleus is compressed and situated next the membrana 
propria. 

Corpora Cavernosa. 
Each corpus cavernosum is surrounded by dense tendinous connective-tissue the 
albuginea, which also contains unstriped muscle cells; around this is loose connective- 
t.ssue containing fat cells, a plexus of nerve branches, and Pacinian corpuscles The 
matrix of the corpus cavernosum consists principally of unstriped muscle tissue, to which 
is added a limited amount of fibrous connective-tissue and elastic fibrils The bundles 
of unstriped muscle tissue form thicker or thinner septa and trabecule connected into 
a plexus. These masses surround and separate the huge venous vessels, the sinuses or 
cavernae, anastomosing into a dense plexus. Each of these vessels is lined with a 
angle layer of flattened endothelial plates. The arterial branches, ensheathed in the 
muscular trabecule of the matrix of the corpus cavernosum, break up into a rich net 
work of capillaries, also situated in the matrix. These capillaries discharge their blood 
in two directions : (.) into the above sinuses or cavernae (Langer) ; and (*) directly 
into the efferent venous branches. The arteriae helicinae of H. Muller, which formerly 



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STRUCTURE OF CORPUS CAVERNOSUM. 281 

were supposed to open freely into the cavernae, are due to a peculiar convoluted and 
twisted condition of the arterial branches, owing, of course, to the contracted state of 
the muscular matrix, while the caverns are collapsed (Henle, Langer, and others). 
In the peripheral, or cortical, part of the corpora cavernosa penis there exists, in addition, 
a direct communication between very fine arterioles and the cavernae (Langer). 

The corpus cavernosum urethrae consists of an inner and outer section ; the 
former is a plexus of longitudinal veins of exactly the same nature as that mentioned 
above of the pars membranacea, with which it forms a direct continuity ; in connection 
with it are the capillaries belonging to the mucous membrane of the urethra. The outer 
section is a real corpus cavernosum, like that of the penis, and is continued as the 
bulbus. 

The cavernae of the corpus cavernosum of the glans penis are also venous vessels 
connected into a plexus ; into the cavernse open the capillaries. These form a dense 
network, situated in the matrix between the cavernae. The cortical layer of this corpus 
cavernosum is in direct communication with the vessels of the mucous membrane of 
the glans. This is a delicate connective-tissue feltwork covered with stratified pave- 
ment epithelium ; numerous conical papillae, containing capillary loops, extend from the 
former into the latter. 

At the corona glandis exist generally small sebaceous glands, the glands of Tyson, 
continued from the inner lamella of the prepuce (see Skin). 

A rich plexus of lymphatics, terminating as a network of fine vessels underneath the 
epithelium, is present in the tissue of the glans, including the papillae. 

Numerous isolated and small bundles of medullated nerve fibres are to be met with 
connected in a plexus. From these come off non-medullated nerve fibres forming a 
dense subepithelial network. For their termination in the epithelium and in end bulbs 
see a former chapter (XVIII.). 

PLATE XXXIX. 

Fig. I. From a vertical section through the testis of the dog. Magnifying power 
about 50. 

c. Capsule consisting of an outer layer, the tunica adnata, and an inner, the tunica 
albuginea. Lymph vessels are indicated between the two layers. 

b. Large blood-vessel in transverse section. 

s. Seminal tubules cut in different directions. 

/. Lymph spaces around and between the tubes. 

Fig. II. From a section through the epididymis of the dog. Magnifying power 
about 50. 



2 82 ATLAS OF HISTOLOGY. 

c. Capsule containing lymphatic vessels in transverse section, injected with Berlin 

blue. 

/. The tubules of the coni vasculosi cut in different directions ; the ciliated columnar 
epithelium lining them is just indicated. Between the tubes are the injected lymphatic 
vessels. 

Fig. III. From a section through the testis of the cat. Magnifying power about 250. 

s. Seminal tubules in section, the lining epithelium is not represented. 

b. Part of a large vein filled with blood corpuscles. 

c. A lamella of the interstitial connective-tissue seen from the surface ; it appears as 
a hyaline membrane — in reality, an endothelial membrane — to which are attached minute 
bundles of connective-tissue fibres. 

c. The same lamellae seen in profile ; owing to the low power the distinction into 
endothelial membrane and connective-tissue fibres is not visible. 

i. Intertubular or interstitial epithelial cells (see the text). 

j. The same seen from the surface. 

The spaces between the above lamellae and between these and the seminal tubes 
are lymph spaces, being the rootlets of the lymphatics of the testis. 

Figures IV. — IX. represent portions of the wall of seminal tubules of the testis of 
the dog. In each of the figures the whole thickness of the wall is shown, viz. from 
the membrana propria to the lumen of the tube. Magnifying power 450. 
m. Membrana propria of the tubule. 

d. The lining epithelium ; in this are to be distinguished the outer seminal cells 
next the membrana propria, then the inner seminal cells ; some of the former and all the 
latter show their nucleus and its intranuclear network of a nature that indicates division 
(compare fig. X., and see also the text of this chapter). Next the lumen are loosely 
connected small epithelial cells, derived by division from the inner seminal cells ; they 
are the daughter cells or spermatoblasts. Their nucleus contains a reticulum. 

e. Endothelial membrane belonging to the intertubular connective-tissue. Between 
this and the membrana propria is a lymph space. 

Fig. V. 

d. Seminal cells. 

1. Spermatoblasts; these are the changed daughter cells next the lumen (see pre- 
ceding figure). 

2. Earliest stage in the formation of the spermatozoa from the spermatoblasts. 

3. Spermatozoa, somewhat further developed. 

Figures VI. VII. and VIII. show the further development of the spermatozoa; 
the peculiar grouping of them is well brought out. 



CHANGES IN NUCLEI OF SEMINAL CELLS. 283 

d. Seminal cells. 

s. Spermatozoa. 

Fig. IX. shows well the peculiar change of the nucleus of the seminal cells during 
and after division. In the layer n the network in the nucleus of the seminal cells shows 
the arrangement peculiar to division (see the text). 

Fig. X. shows various forms of nuclei of the seminal cells under a higher power than 
represented in the preceding figures. 

a is a ' resting ' nucleus of one of the outer seminal cells. 

b are nuclei preparatory to division ; they have no membrane, and the contents are 
a beautiful ' convolution ' of relatively thick fibrils or rods viewed in different directions. 

c, similar nuclei, in which the fibrils radiate towards a central line ; this form 
gradually leads to that of the 'wreath' and 'aster,' the radiation of the fibrils being 
towards a central point instead of a line. 

d is a similar nucleus, but its fibrils, being arranged vertically to the plane of the 
microscope, are almost all seen in optical transverse section. They are limited to the 
periphery of the nucleus, and run more or less parallel with one another, ' basket- 
shaped ' arrangement. 

Fig. XI. Two groups of similar nuclei of testis of the cat ; each of these groups is 
contained in one large cell, the substance and outline of which are not shown here. 

The nuclei in each group are arranged in a spherical zone ; the left group is seen 
from the top, the right one from the side. 

The fibrils in the different nuclei have a variable arrangement, as 'convolution/ 
'basket/ or 'aster.' 

Fig. XII. From the same testis as the preceding figure, showing one large and 
three small seminal cells ; the former has several, the latter each one irregular, lobed, 
homogeneous nucleus. Whether or not this uniformity in the substance of the nuclei 
and their lobed form is due to shrinking, or whether or not in reality these nuclei show 
similar fibrillar contents as those of the preceding figures, it is not possible definitely to 
ascertain. Magnifying power about 450. 

Fig. XIII. From a vertical section through the glans penis of a newborn child ; the 
blood-vessels are injected with Berlin blue. Magnifying power abouf 25. 
e. Stratified epithelium of the surface of the glans. 

m. Mucous membrane, possessed of numerous minute papilla? with networks of 
capillaries. Numerous transparent (empty) lymphatic vessels are indicated in the tissue 
of the mucous membrane. 

eg. Corpus cavernosum, showing the network of venous sinuses or cavernae connected 
with the capillaries of the stroma. 

u u 



284 ATLAS OF HISTOLOGY. 

The vessels of the mucous membrane of the glans communicate with the vessels of 
the corpus cavernosum. 

cu. Corpus cavernosum urethra. 

u. Urethra ; its mucous membrane is lined here with stratified pavement epithe 

Hum. 

c The epithelium is much thinner, being composed of columnar cells. 

The mucous membrane is possessed of minute papillae, containing loops of the net- 
work of blood capillaries. These are in connection with the venous sinuses of the corpus 
cavernosum urethree. 



285 



CHAPTER XXXII. 

THE FEMALE GENITAL ORGANS, 

The Ovary. 

The framework of the human ovary, as well as that of mammals, consists of (a) the 
tissue of the hilum, and (6) the stroma of the parenchyma. 

a) The first is loose fibrous connective-tissue, extending also into the parts con- 
taining the Grafian follicles, that is, into the parenchyma, or zona perenchymatosa of 
Waldeyer. It is very rich in big vessels, and may be therefore called, with Waldeyer, 
the zona vasculosa. Numerous bundles of unstriped muscle cells pass from the li^amen- 
tum latum into this zona vasculosa, and accompany the blood-vessels as longitudinal 
bundles. Some of them enter also the parenchyma. 

6) The stroma of the parenchyma is a very peculiar tissue, consisting of bundles of 
shorter or longer transparent spindle-shaped cells, each with an oval nucleus. There is 
a very small admixture of fibrous connective-tissue, brought in chiefly with the vascular 
branches. The ovaries are, in this respect, subject to great variations, for in some cases 
(cat, dog) there is very little to be seen of such bundles, while in others (man, rabbit) 
we meet with bundles of connective-tissue, in some places of considerable size. The 
above bundles of spindle-shaped cells cross each other in many ways, and thus form a 
tolerably dense tissue. 

According to the distribution of the parenchyma, that is, the Grafian follicles, the 
stroma forms larger or smaller continuous masses. There is generally in the cortex 
of the ovary a layer of stroma of appreciable thickness, not containing any ova ; this 
layer is the albuginea of Henle. In man this albuginea shows a distinction into an outer 
and inner longitudinal and a middle circular layer of connective-tissue (Henle). In 
many mammals it consists only of bundles of spindle-shaped cells, which extend 
either longitudinally or obliquely. In the cat the bundles of the albuginea are grouped 
as a superficial thin longitudinal layer, underneath which in many places is a deep circular 
or slightly oblique layer. Around the larger and largest Grafian follicles the stroma of 
spindle-shaped cells is arranged in more or less concentric layers. 

Between the spindle-shaped cells also branched cells are to be met with ; they 
are elongated, each with an oblong nucleus, their processes pass in a longitudinal 

U U 2 



2 86 ATLAS OF HISTOLOGY. 

direction amongst the spindle-shaped cells, and anastomose by lateral branchlets into a 
network. 

It is difficult to definitely ascertain the nature of the spindle-shaped cells, viz. 
whether they are imperfectly developed connective-tissue or unstripecl muscle cells. 
They certainly resemble unstriped muscle cells more than anything else. While 
Kolliker, Henle, Pfluger, Waldeyer, v. Winiwarter, and others regard the stroma as 
composed of connective-tissue, Rouget, Aeby, Klebs, and others assume a great amount 
of unstriped muscular tissue in it, while His considers the stroma almost enttrely 
muscular. 

Between the bundles of the spindle-shaped cells are seen from place to place smaller or 
larger cylindrical or irregular more or less anastomosing groups of small polyhedral cells, 
each with a spherical nucleus. The substance of these cells is a very fine reticulum ; the 
nucleus contains also a reticulum, and in some instances contains one or more thickenings, 
nucleoli. These cells are most numerous in the deeper parts of the parenchyma ; they 
are generally absent from the albuginea ; they extend also into the tissue of the hilum, 
where they have been seen by Kolliker, but misinterpreted by this observer. Their 
significance is exactly the same as that of the intertubular or interstitial epithelial cells 
mentioned in the testis, viz. they are remnants of the epithelium of the Wolffian body, 
and we shall call them, therefore, interstitial epithelial cells. They have been known 
through His, Waldeyer, Romiti, Born, Balfour, and many others. Balfour has very 
distinctly traced them from the Wolffian body, and he describes them as the ( tubuliferous 
tissue ' in the developing ovary. 

The interstitial epithelial cells are well shown in the ovary of the cat, the dog, and 
the guinea pig, where they are easily recognised, besides by their shape, also by a slight 
yellow tinge. 

The free surface of the ovary is covered with a single layer of columnar or short 
columnar epithelial cells, each with an oval nucleus ; this is the germinal epithelium of 
Waldeyer, who first showed the great contrast of this epithelium and the layer of 
flattened endothelial cells covering the ligamentum latum ; a similar contrast exists 
between the columnar (ciliated) epithelium of the oviduct and the flattened endothelium 
of the peritoneum around the abdominal extremity of the former. 

The parenchyma consists of the Grafi an follicles. These are of very various sizes 
and shapes, and are so distributed that the larger ones are seated in the deeper parts of 
the zona parenchymatosa, while the small ones lie near the surface, immediately under- 
neath the albuginea. In most instances the latter are aggregated as smaller or larger 
groups ; in some cases (cat and rabbit, Waldeyer) these groups are so close that they 



GRAFIAN FOLLICLES. 2 $ ? 

form almost a continuous layer two or three deep underneath the albuginea, the cortical 
layer of Schronn. This has been found (Romiti) to be the case in all mammals. From 
the superficial layer of small Grafian follicles to the deep-seated big ones are all gra- 
dations. The small Grafian follicles are generally spherical, the middle-sized ones sphe- 
rical or oblong, and the largest are spherical, or more or less elongated or irregular ; 
the last-named are possessed of one, two, or more prolongations (see below). As 
mentioned above, the bundles of spindle-shaped cells of the stroma pass in between and 
around the Grafian follicles, both where they are in groups and isolated ; the amount 
of stroma is of course greater between the groups than between the individual follicles 
of a group. The spindle-shaped cells possess a more or less distinct concentric arrange- 
ment around the large Grafian follicles, thus forming a special outer membrane for the 
latter ; this is the tunica fibrosa of Henle. ' The larger the follicle the more developed is 
the network of blood capillaries in this outer tunic. 

Each Grafian follicle, including the smallest, is limited by a mcmbrana propria (Kol- 
liker, Foulis, Balfour and others), which is thicker in the larger follicles than in the 
smaller ones. It contains here and there a flattened oval nucleus, which appears staff- 
shaped when viewed in profile. Inside the membrana propria are the epithelial cells, 
or the membrana granulosa of the Grafian follicle, and in the centre of the follicle is the 



ovum, 



In the smallest follicles, that is, in those next the albuginea, the membrana propria 
is a very delicate membrane, and between it and the ovum is a single layer of trans- 
parent and very flattened cells, each with a flattened or spherical nucleus. The ovum 
appears here as the most conspicuous part. In the follicles of the next size, the epithe- 
lium lining the membrana propria also consists of only one layer, but its cells are poly- 
hedral, each with a spherical nucleus. Then follow follicles whose epithelium is composed 
of columnar cells still in one layer. In the next larger follicles the cells are in more than 
one layer, and in the largest they are in three, four, or more layers. The outermost 
cells, viz. the cells next the membrana propria, are distinctly columnar, placed vertically, 
and each contains an oval nucleus ; those of the other layers, however, are smaller, 
transparent, and polyhedral, each with a spherical nucleus. 

The cells are separated from one another by a linear interstitial cement-substance. 
In well preserved specimens there is a very delicate reticulum to be met with in this 
cement-substance ; its meshes differ greatly in size, in some places they are not larger than 
one cell, in others each contains several cells. A f&w oval or angular or irregularly 
shaped nuclei maybe found in this reticulum. It stretches from the membrana propria 
inwards, and in all probability is analogous to the nucleated reticulum of the seminal 
and other gland tubes, mentioned on former pages as supporting the epithelial cells. 



288 ATLAS OF HISTOLOGY. 

In the fully formed Grafian follicle the ovum is embedded in a mass of epithelial 
cells, projecting like a mound from the epithelial lining of the follicle into the cavity 
of the latter. This mass is the discus or cumulus proligerus ; the cavity contains an 
albuminous fluid, liquor folliculi. In some follicles there may be two or even three such 
cumuli, each containing an ovum. 

The epithelial cells of the discus proligerus are, like the cells of the membrana gra- 
nulosa, small transparent polyhedral or elongated cells ; but those immediately around 
the ovum are beautifully columnar, each with an oval nucleus. 

All transitional forms exist between the above ripe follicles and the small follicles, 
which do not contain any cavity yet, but in which the ovum is placed more or less cen- 
trally, the space between it and the membrana propria being filled with epithelial 
cells. The transition is effected by the appearance of albuminous fluid in small isolated 
cavities amongst the epithelial cells of the membrana granulosa, or between the ovum 
itself and the epithelium ; in the latter case the ovum remains surrounded by the epithelial 
cells, discus proligerus. These cavities gradually increase in number and size, and be- 
come confluent, the follicle thus greatly enlarges, and the ovum, embedded in the 
discus proligerus, is pressed to one side and remains connected on this side with the 
membrana granulosa. 

While this fluid appears, both the epithelial cells immediately surrounding the ovum, 
as well as those of the membrana granulosa, greatly increase in numbers. 

In many follicles, containing a greater or smaller quantity of the liquor folliculi, we 
notice in this latter small cells, isolated or in small groups, more or less vacuolated. 
They are vesicular structures, containing a cavity surrounded by a thin membrane, the 
original cell-substance, at one point of which lies a spherical or slightly compressed 
nucleus. These cells are probably epithelial cells that have become separated from the 
follicular epithelium and are undergoing retrogressive changes (maceration). They 
gradually fade away entirely. 

In connection with, or contiguous to, middle-sized and large Grafian follicles may 
be seen larger or smaller solid cylindrical, or oval, or irregularly shaped masses. These 
masses are limited by a membrana propria, and when they are connected with a Grafian 
follicle, their membrana propria is a continuation of the same structure of the Grafian 
follicle ; they consist of more or less columnar transparent epithelial cells, of exactly 
the same characters as those of the granulosa of the Grafian follicles, with which in 
some instances they are distinctly continuous. These masses are very well shown in the 
ovary of the rabbit. Whether all apparently isolated solid masses of similar cells, in 
a section through the ovary, are in reality isolated or not, i.e. whether or not they are 
connected with a Grafian follicle, but owing to the direction of the section this connection 



STRUCTURE OF OVUM. 2 g 9 

is not visible, it is impossible to say. They are not to be confounded with the groups 
of interstitial epithelial cells mentioned on a former page ; both differ in shape, size, ar- 
rangement, and appearance. 

Not all those masses that are connected with a Grafian follicle are solid prolonga- 
tions of the epithelium of this latter; some show a small cavity, are therefore tubular, 
and still others, being at the same time larger, contain an ovum. Some of the large 
Grafian follicles are possessed of one or two solid prolongations, others, in addition, 
communicate with one or two small follicles each with an ovum. In the latter case 
we find, then, two or three Grafian follicles in open communication with one another ; 
they are either very different in size (development), one or two being comparable to a 
small or middle-sized follicle, while the third may be a fully developed one ; or they 
appear of nearly the same size. The communication may be through a narrow neck, as in 
some, or wide open, as in other instances. The Grafian follicles with two or three 
ova are only modifications of the last-named plan (see below). 

The ovum is a nucleated cell, varying in size according to the size of the follicle. 
In the smallest follicles the substance of the ovum is in immediate contact with the flat 
epithelial cells of the Grafian follicle ; but in the follicles of the next larger sizes, that 
is, whose epithelial cells are polyhedral or even columnar, there is a distinct bright 
membrane, zona pellucida, surrounding the substance of the ovum. The larger 

o 

the ovum the thicker the zona pellucida. In all cases, from the smallest follicles 
that contain a zona pellucida to the fully formed ones, in which the ovum lies in 
its discus proligerus, the outer surface of the zona pellucida appears to form a 
direct continuity with the interstitial cement-substance, between the epithelial cells of 
the follicle ; hence, when the outer surface of the zona pellucida is seen in the bird's- 
eye view, it shows the outlines or impressions of the surrounding epithelial cells. This 
connection of the zona pellucida with the interstitial substance seems to indicate that 
the former is a product, a cuticular excretion, of the epithelial cells themselves. The zona 
pellucida of the ripe ovum shows a very fine (vertical) striation, which, according to Pfiuger, 
Leydig, and Waldeyer, is due to the substance of the epithelial cells, immediately surround- 
ing the zona pellucida, being continuous as fine rods or threads into the latter membrane. 

The substance ot the ovum is very transparent ; in the large ova it contains the 
yolk granules. In sections through the hardened ovary of the rabbit, dog, cat, guinea 
pig, the protoplasm contains a more or less distinct reticulum of fine fibrils. 

In the larger ova the protoplasm surrounding the germinal vesicle is generally more 
transparent than that next the zona pellucida (Pfluger). These two substances also 
stain differently in osmic acid (Romiti). 

The nucleus or germinal vesicle of the small ova, i.e. those next the albuginea, 



2 9 o ATLAS OF HISTOLOGY. 

is generally single, rarely it is double ; it contains within a definite membrane a trans- 
parent matrix, and in it a delicate reticulum of fibrils, in some cases without any, in 
others with one or more irregularly shaped large clumps, nucleoli or germinal spots ; 
this reticulum has been noticed by Balfour also in the young ovary. 

The reticulum is very distinct if the ovary has been prepared with chloride of gold. 
In specimens hardened in the ordinary way (Midler's fluid) the germinal vesicle 
appears homogeneous with faint and fine granules, it stains more or less uniformly in 
dyes ; in it are situated, generally peripherally, one or two or more bright spherical or 
angular clumps — germinal spot or spots. 

The larger and largest ova contain generally one, seldom two, nuclei or germinal 
vesicles, whose structure does not differ from that of the small ova. In the fresh state 
and after some hardening reagents, e.g. Mailer's fluid, the germinal vesicle shows only 
faintly the intranuclear reticulum ; this comes out much more prominently in chloride of 
gold specimens. 

Many follicles arrive at the stage of ripeness before puberty is reached, and are sub- 
ject to a process of degeneration. But this process involves also follicles of earlier 
stages, and even the smallest follicles (Pfluger, Waldeyer, and others). It differs, how- 
ever, according to Slavjansky, from the normal process by which a ripe Grafian follicle 
is converted, after puberty, into a corpus luteum. 

The degeneration leading to the formation of a corpus luteum consists in a multipli- 
cation of the epithelial cells of the membrana granulosa, and in the sprouting of new 
capillary blood-vessels, with migratory cells, from outside the follicle into its hyper- 
trophied epithelium. This new growth stands in a causal relation to the discharge of 
the ovum (Spiegelberg), and the cavity of the follicle is gradually filled up with the 
hypertrophied epithelium, with pigment granules and blood-vessels. The tissue now 
occupying the centre soon changes into gelatinous tissue. The cortical portion of the 
corpus luteum so much hypertrophies that it becomes gradually folded, and its cells 
undergo fatty degeneration, becoming filled with several small fat-globules, which gra- 
dually become confluent into one large drop ; the nucleus is hereby pressed into the 
periphery of the cell. 

The degeneration which occurs in Grafian follicles before puberty is similar to the 
above, but differs from it in the fact that the hypertrophy and fatty degeneration of the 
granulosa and the number of capillary blood-vessels in it are not so great. The 
vascular gelatinous tissue, occupying the centre of a corpus luteum, formed before 
puberty, remains separated for some time from the cortical portion of the latter by 
the persistence of the zona pellucida of the ovum. Good examples of degenerating 
follicles of this nature are to be met with in the ovary of halfgrown rabbits. 



DEVELOPMENT OF OVARY. 2gi 



Development of the Grafian Follicles and Ova of Mammals. 

In this I shall follow Balfour's account given in No. Ixxii. (October r8 7 8) of 
the ' Quarterly journal of Microsc. Science ; ' for I have been able to convince myself of 
the accuracy of his observations. 

The germinal epithelium of the early foetal ovary undergoes a very rapid increase 
in thickness owing to the division of its cells. The division of the nucleus is here also 
associated with similar changes in the intranuclear network, as described in the testis 
and as will be treated in detail in a future chapter ; of these changes Balfour noticed 
some, e.g. the convolution and the aster. 

The thickened epithelium becomes so permeated by the vascular stroma (embryonal 
connective-Ussue), that the former, viz. the epithelium, is transformed into a honey 
combed mass ; this consists of irregularly shaped groups or nests of cells connected 
with each other and with the cells of the surface. These nests are largest in the depth 
and smallest near the surface. 

According to Waldeyer these changes are brought about by a mutual ingrowth of the 
germinal epithelium and the stroma ; but, according to Balfour, the segregation into nests 
is indicated already before the ingrowth of the stroma takes place, and it is the stroma 
alone that grows into the former, and thus produces the permanent separation of the 
nests. But in this, I think, Balfour goes too far. 

The separation of the nests from the external layer of the epithelium, viz the one 
persisting on the surface as the germinal epithelium, by the formation, from the 
vascular stroma, of a tunica albuginea, takes place only very gradually. Even some 
time after birth, some superficial nests appear still connected with the germinal epithe- 
lium, Pfluger's ovarial tubes. 

But many of the apparent prolongations of the germinal epithelium of the surface 
into the stroma, to be noticed in sections long after birth (Pniiger, Waldeyer, and 
others), are not in reality outgrowths of that epithelium, but are due to folds and ir- 
regularities of the surface (Foulis, Balfour). 

The small or external nests give origin to the cortical layer of small Grafian follicles 
of the fully developed ovary (see a former page), whereas from the deeper-seated nests 
are developed the larger follicles. 

Some of the epithelial cells of the germinal epithelium, already in the earliest stages, 
enlarge and become converted into primitive ova (Waldeyer), and similar changes con- 
tinue to occur in the nests, in the smaller superficial as well as in the larger deep ones 
(Balfour), viz. some of their cells become enlarged and converted into primitive ova. 

x x 



292 ATLAS OF HISTOLOGY. 

These, viz. the ova, undergo division, as is evinced by the characteristic changes of 
their intranuclear network, but they appear also to become fused into a perinuclear 
mass, which afterwards again divides into several ova (Balfour). Their products, by 
enlargement of the nucleus and cell, and by the substance of the latter becoming 
more distinct, change into the permanent ova. The nucleus of these, as Balfour 
correctly described, possesses a characteristic reticular structure. 

Each nest contains a number of ova. The epithelial cells of the nests which are 
not converted into ova serve for the formation of the epithelium of the Grafian follicle. 
In the small nests, viz. in those of the cortical layer, the epithelial cells are relatively few 
and small, and by multiplication they gradually increase in number, sufficient to form 
an epithelial investment around each ovum. By an ingrowth of the stroma, the ova 
with their epithelial coat become separated from the rest of a nest, and then outside 
each a delicate membrana propria is formed. In some places the nests, being connected 
with one another, form more or less cylindrical masses, and the ova appearing in 
them have a chainlike arrangement, ovum-chains of Pfluger. 

A similar change occurs also in the larger or deep nests, viz. the epithelial cells 
undergo multiplication, and many of the ova become gradually invested in their own 
layer of epithelial cells ; these are at first polyhedral, but, as development proceeds, be- 
come more or less columnar. By the ingrowth of the stroma, the follicles become sepa- 
rated from one another, each containing one or two ova. A membrana propria soon 
appears around them. 

It is to be noticed that, owing to a continued multiplication of the epithelial cells 
constituting these nests, larger or smaller portions of them (nests) remain without any 
ova. They may persist connected with a Grafian follicle or not. The masses of 
epithelial cells, which we described on a former page as cylindrical or irregular groups of 
epithelial cells, isolated, or connected with a Grafian follicle, receive thus a ready explana- 
tion. 

Whether an increase of these epithelial masses takes place also in the adult, and 
whether some of their cells change into ova also some time after birth, are points 
difficult to decide, but all appearances are in favour of such a view, and Balfour's 
observations very much support it. Bischoff, Waldeyer, and others are of opinion 
that no ova are formed after birth ; but Pfluger, Kolliker, and others hold the 
contrary view. According to Foulis, no new ova are formed in the human ovary two 
and a half years after birth. 

There can be then no doubt that both ovum and epithelium of the Grafian follicle 
are derived from the primary germinal epithelium ; Foulis maintains that only the ovum 
has such an origin, while the epithelium of the Grafian follicle is derived from 



TERMINATION OF VESSELS AND NERVES. 293 

the stroma ; but in this he is at variant ™\tU ^n 

at variance with all recent investigators, as Pflfiger 

Waldeyer, Romiti, Balfour, and many others. 



The human parovarium, or organ of Rosenmuller, consists of a number of tubes 
s.tuated ,n the ligametum latum, or extending into the hilum, as is the case in many 
mammal, The tubes are lined with columnar ciliated epithelial cells in the human sub- 
ject, in the dog they are lined with polyhedral cells (Waldeyer). 



The termination of the blood-vessels is in a dense capillary network around the larger 
follicles, but the albuginea as well as the stroma contain numerous capillary vessels 

According to His, the lymphatics form, in the hilum, a network of tubes with valves 
and are connected with lymph spaces that surround a greater or smaller part of the 
periphery of the large Grafian follicles. 

Waldeyer traced very fine medullated new fibres into the parenchyma, where they 
are lost amongst the larger Grafian follicles. 

According to Elischer, there is a network of non-medullated nerve fibres in the 
stroma of the ovary. The outer membrane of the large Grafian follicles possesses a 
distinct network of fine nerves with wide meshes ; in connection with this is a dense 
network of fine varicose nerve fibrils placed closely against the membrana granulosa 



The Oviduct. 



The wall of the oviduct, including the fimbria of the infundibulum, is composed 
of a mucous membrane, a muscular coat, and an outer adventitia, the peritoneum. 

The mucous membrane is a dense connective-tissue feltwork, containing a rich 
network of capillary blood-vessels ; on its inner free surface it is covered with columnar 
epithelium ; the cells are conical and ciliated, and between them are wedged in spindle- 
shaped or inverted conical cells (see Chapter II.). The mucous membrane is placed 
in longitudinal or complex folds, and at the base of the folds there are more layers 
of the epithelium than at their top. 

The mucous membrane does not contain any glands, neither in man nor in other 
mammals. In sections through the ampullar portion there appear depressions of the 



X X 2 



2 94 ATLAS OF HISTOLOGY. 

epithelium into the mucous membrane, but these are due to the folds cut in various 
directions. Hennig, however, maintains the existence of tubular glands in the human 
oviduct as well as in that of mammals. 

The muscular coat is composed of bundles of unstriped muscular cells, arranged pre- 
eminently circularly. There are, however, more externally oblique or even longitudinal 
bundles to be met with. 

The adventitia is a connective-tissue membrane with networks of elastic fibres. 

The Uterus. 

As in the oviduct so also in the uterus the wall consists of a mucous membrane, 
a muscular coat, and an outer adventitia, the peritoneum. 

The epithelium covering the free surface of the mucous membrane is a single layer 
of shorter or longer ciliated columnar cells, each with an oval nucleus. These cilia are 
very perishable, for soon after death and after hardening they are very difficult to 
recognise. Friedlander found in the human uterus the whole cavity of the uterus and 
the canal of the cervix lined with ciliated columnar cells. This columnar ciliated epi- 
thelium commences, according to Lott, in children in about the middle of the cervix ; in 
adults it reaches to the ostium externum. The surface of the portio vaginalis is 
covered with stratified pavement epithelium. This is thinnest where the mucous mem- 
brane passes into that of the vagina ; it gradually increases in thickness towards the 
ostium uteri externum, and just before this is reached the epithelium is thickest. Into 
the stratified pavement epithelium extend minute papillae from the subjacent mucosa. 

The mucous membrane differs greatly in structure and appearance in the cervix 
and in the fundus. 

a) In the cervix it is a dense connective-tissue membrane arranged in a number of 
permanent folds, the palmae plicatae. Few and thin bundles of unstriped muscle cells 
penetrate from the outer muscular coat into the mucous membrane. Between, and in the 
palmae plicatse, are minute glands whose membrana propria is intimately connected 
with the connective-tissue of the mucosa. These glands are shorter or longer 
cylindrical or irregularly shaped tubes, possessed of a large lumen and lined with a single 
layer of columnar cells, which, in the newborn child at any rate, are ciliated. According 
to Friedlander, however, they are polyhedral and non-ciliated. Some of the epithelial 
cells are goblet cells (Friedlander, Wyder). 

In the adult these gland tubes are longer than in the newborn child, owing to the 
mucous membrane being much thicker in the former than in the latter. 

According to Kolliker, Hennig, Tyler Smith, and others, the mucous membrane 
of the cervix, in the lower portion, projects beyond the general surface in the shape of 



STRUCTURE OF UTERUS. 2g5 

minute long and thin papilla, covered with ciliated epithelium, like the general surface, 
and each containing a loop of capillary vessels ; but, according to Henle, with whom I 
agree, these -papillae' are in reality only sections through the septa or folds of the 
surface. 

6) In the fundus the mucous membrane contains, according to Leopold, fibrous 
connective-tissue, in the shape of a spongy or honey-combed plexus of fine bundles, 
covered with endothelial plates of various sizes, each with an oval flattened nucleus. 
These endothelial plates are connected into more or less continuous membranes. 
The spaces of the spongy matrix are lymph spaces; glands and blood-vessels are 
situated in them. The endothelial plates form lamellated sheaths around the blood- 
vessels and glands (Leopold). Between the endothelial membranes exist also branched 
cells, connected by their processes into a network (Wyder). Most observers, in- 
cluding Friedlander and Leopold, mention bundles of unstriped muscular tissue pene- 
trating into the mucous membrane from outside, viz. from the muscular coat, but in 
the uterus of the newborn child I fail to detect them, except in the immediate vicinity 
of the muscular coat, and according to Kundrat and Engelmann there are no mus- 
cular bundles to be found in the mucous membrane of the adult uterus. 

An important constituent of the mucous membrane are the glands, glanduke 
uterinae. In the newborn child they are limited chiefly to the sides. They are 
short and branched, and their number increases towards puberty, new glands being 
formed by tubular ingrowths of the surface epithelium (Kundrat and Engelmann). 
The glands are simple tubular glands ; they are wavy, slightly convoluted or spiral, and 
terminate in the depth of the mucous membrane either as a single or branched caecal 
dilatation. In the dog the glands are of two kinds, single and compound tubular 
(Sharpey). 

Each gland tube possesses a delicate membrana propria, which is an endothelial 
membrane (Leopold) ; and this is lined with a single layer of columnar, pyramidal, or 
conical epithelial cells, each with an oval nucleus, situated in the outer third of the cell 
(Lott, Goroschankin). The epithelial cells are ciliated. This had been seen first in the 
glands of the sow by Allen Thomson, and afterwards by Nylander ; in man by Fried- 
lander, and in many domestic animals (cow, sheep, rabbit, mouse, &c.) by Lattaud, 
Ercolani. The cilia are very perishable, and in hardened specimens very difficult to see. 
Goroschankin maintains that in the glands of the dog and the cat the lining columnar 
epithelial cells are without cilia. 

Comparing these glands in the newborn child and in the adult, it will be seen that 
they are (absolutely and relatively) much longer in the latter case. 

During menstruation and in pregnancy the glands greatly increase in length. 



29 6 ATLAS OF HISTOLOGY. 

The Ieno-th of the glands varies in different animals and in the different parts of 
the same uterus. The mucous membrane of the uterus of the kangaroo, owing to its 
very great thickness, contains unusually long gland tubes (Turner). 

According to Kundrat and Engelmann, the thickness of the mucous membrane 
becomes increased during menstruation, the epithelium of the surface and that of 
the greater portion of the glands being destroyed by fatty degeneration and finally 
altogether detached ; its restitution takes place from the epithelium of the deeper 
portion of the glands ; but, according to S. Williams, not only the epithelium but also 
the greater part of the mucous membrane is destroyed by fatty degeneration. Wyder 
confirms this. 

The muscular coat forms the chief part of the wall of the uterus ; its bundles are 
entirely composed of unstriped muscular cells. Their (bundles) arrangement is very 
different in different parts of the uterus, but on the whole they are arranged, in the 
fundus of the normal human uterus, in three strata (Henle) : 

a) An outer thin stratum, next the peritoneal covering, its bundles are longitudinal ; 
towards the middle stratum there appear between them oblique bundles. 

b) A middle coat, the prevalent direction of its bundles is circular, but there are 
numerous small longitudinal bundles between them. 

c) An inner stratum whose bundles run obliquely and transversely. 
The inner and middle coat are of almost the same thickness. 

In the cervix the muscular coat is thinner ; the muscular bundles are also arranged 
in three strata (Henle), an outer and inner longitudinal and a middle circular layer. 

The outer longitudinal bundles pass from the uterus into the muscular coat of the 
adjoining organs, viz. the oviduct, ligamentum teres, and vagina. 

The muscular bundles in all strata anastomose with one another into plexuses, and 
are separated from one another by a scanty connective-tissue ; this is better seen in the 
inner and middle than in the outer stratum. The connective-tissue consists of fibrous 
lamellae separated from one another by endothelial membranes. Numerous lymph clefts 
and lymph vessels are contained in this intermuscular connective-tissue (Leopold). 

In the inner stratum, next the mucous membrane, the intermuscular connective- 
tissue assumes the character of that of the latter. 

In the uterus-horns of mammals the muscular coat is generally composed of an outer 
longitudinal stratum and an inner thicker circular stratum, but the bundles of the former 
pass as oblique bundles into the latter. Also the inner bundles of the inner stratum 
possess in many places a more or less oblique direction. 

The arterial trunks penetrating through the muscular coat into the mucous mem- 



BLOOD-VESSELS OF UTERUS. 2g7 

brane break up into capillary networks for the glands and for the subepithelial layer of 
the mucous membrane. In the muscular coat the arteries terminate in networks of 
capillaries for the muscular bundles. 

The arterioles entering the mucous membrane of the cervix and its capillaries are 
distinguished by the great thickness of their wall (Henle). 

The arrangement of the venous vessels of the anterior and posterior side of the 
fundus is, in the normal uterus of the child at any rate, of a peculiar nature, viz. : near the 
peritoneum, and more or less embedded in the outer muscular stratum, is a plexus of 
relatively small veins, running chiefly in a longitudinal direction, but the middle stratum 
contains huge venous sinuses or cavern* more or less longitudinally arranged and 
connected into a plexus. 

The wall of these venous sinuses is composed, as usual, of an endothelial membrane, 
and outside this is a very thin connective-tissue membrane, but the plexuses of small 
bundles of the muscular coat give to these sinuses a powerful support, for they sur- 
round them as circular or longitudinal or oblique bundles, the first being predominant 
These venous sinuses are in open communication, on the one hand, with the capillary 
blood-vessels of this stratum of the muscular coat, and, on the other, with the plexus of 
smaller veins situated externally, as mentioned above. From this, then, it follows that we 
have here a condition of things analogous to that existing in the corpus spongiosum of 
the urethra, described on a former page ; viz. the capillary blood-vessels discharge their 
blood into large venous sinuses surrounded by, and embedded in, a plexus of muscular 
trabecule ; these sinuses anastomose with a plexus of veins much smaller than them- 
selves. 

This middle stratum with its venous sinuses differs in this respect in a marked 
manner from the inner stratum of the muscular coat, inasmuch as the latter stratum is 
without any venous sinuses and contains only small vessels, both arterial and venous, 
which pass through it in an oblique direction. 

The lymphatics are very numerous ; according to Leopold they are present in the 
mucous membrane as the above-named lymph sinuses lined with endothelium. These 
sinuses are in open communication with lymphatic vessels and lymphatic'clefts situated 
in the connective-tissue of the muscular coat. They form an intercommunicating system, 
and both kinds of lymphatics are lined with an endothelium. In man their arrangement 
is very complex, owing to the complex way in which the muscular bundles are arranged. 
They lead into a subserous plexus of large lymphatic tubes with valves and saccular 
dilatations. In the uterus-horns of mammals the lymphatics of the muscular coat are of 
a more regular arrangement, being pre-eminently longitudinal in the outer, circular 



29 S ATLAS OF HISTOLOGY. 

in the inner muscular coat. Between the two are situated the collecting lymphatics with 
valves. 

According to Lindgren the lymphatics of the mucous membrane of the cervix are 
connected with saccular sinuses extending near the epithelium of the inner surface of 
the mucous membrane. 

The nerves of the muscular coat have the same arrangement and termination as in 
other unstriped muscular tissue (Frankenhauser, Arnold) ; those entering the mucous 
membrane are connected with ganglia (Frankenhauser, Luschka, Koch, Kehrer, and 
others). According to Lindgren the mucous membrane contains a plexus of non-medul- 
lated nerve fibres, which, near the epithelium of the free surface, give off bundles of 

very fine fibrils. 

* 

The Vagina. 

The mucous membrane of the vagina is a dense connective-tissue feltwork, with 
numerous elastic fibrils forming networks. It projects above the general surface in the 
shape of longer or shorter conical or irregular pointed or blunt permanent folds or 
papillae. The epithelium of the free surface is a thick stratified pavement epithelium of 
the ordinary description ; into this the superficial layer of the mucous membrane, viz. 
the mucosa, projects in the shape of long cylindrical or conical simple or divided 
papillae. 

According to v, Preuschen there exist in the mucous membrane tubular glands 
lined at their fundus with ciliated columnar epithelium. Hennig also describes tubular 
glands in the mucous membrane, especially of the fornix and introitus vaginae ; in the 
rest of the organ they are very rare. 

The deeper part of the mucous membrane is loose in its texture, and represents the 
submucosa. 

Outside this is the muscular coat, consisting of an inner circular and an outer 
longitudinal stratum of bundles of unstriped muscular cells. There are oblique bundles 
passing from one layer into the other. Muscular bundles penetrate into the submucosa, 
and further into the mucosa, where they may be traced up to near the epithelium. The 
muscular bundles are separated from one another by a relatively large amount of con- 
nective-tissue. 

Outside the muscular coat is a layer of connective-tissue ; embedded in it is the 
outer plexus of veins, plexus venosus vaginalis. 

The arterial branches entering the mucosa break up into a capillary network from 
which simple or compound loops pass into the papillae. 



BLOOD-VESSELS OF VAGINA. 299 

The variously shaped projections (folds or rugae) above mentioned contain a plexus 
of large veins. The connective-tissue between these vessels includes bundles of 1111- 
striped muscular cells derived from the muscular coat, as mentioned above. We have 
thus an arrangement similar to a cavernous tissue (Gussenbaur). 

A second plexus of veins is situated in the submucous tissue, whose meshes are 
elongated and parallel with the long axis of the vagina. 

The connective-tissue, in which the above-named plexus venosus vaginalis is situ- 
ated, that is the plexus outside the muscular coat, contains numerous bundles of unstriped 
muscular cells derived from the circular stratum, and hence this plexus also resembles 
a cavernous tissue (Gussenbaur). 

The lymphatics form plexuses of fine vessels (capillaries) in the mucosa and of 
large tubes with valves in the submucosa. There are also numerous lymphatic vessels 
connected into networks in the muscular coat. The efferent vessels lead into a rich plexus 
of large lymphatic trunks with saccular dilatations situated in the connective-tissue 
outside the muscular coat. 

The mucous membrane possesses either small well-defined solitary lymph follicles or 
diffuse adenoid tissue (Loewenstein). 

The nerve branches form a plexus, in the nodes of which are contained ganglionic 
swellings. 

The Urethra. 

The epithelium lining the mucous membrane, in the part next the bladder, is a 
stratified transitional epithelium consisting of a superficial layer of short columnar, 
or club-shaped cells, below which are several layers of polyhedral or cubical cells ; 
further outwards, that is nearer the orificium externum, it is a stratified pavement 
epithelium. 

The mucosa is a dense connective-tissue containing rich networks of elastic fibres 
(Robin and Cadiat) and a greater or smaller amount of diffuse adenoid tissue. Numerous 
minute papillae with capillary loops project into the epithelium. 

A great many short simple or compound tubular mucous glands are found in all 
parts of the urethal mucous membrane, the glands of Littre" ; they are analogous to 
those described of the male urethra. 

The deeper or loose section of the mucous membrane, viz. the submucosa, contains 
a plexus of large venous vessels ; the tissue between them contains bundles of unstriped 
muscular cells, and thus resembles cavernous tissue. 

This cavernous tissue is considered by some anatomists (Arnold, Henle, and others) as belong- 
ing partly or wholly to the next outer stratum, viz. the longitudinal layer of the muscular coat. 

Y V 



3 oo ATLAS OF HISTOLOGY. 

The muscular coat consists of an inner longitudinal and an outer circular stratum of 
unstriped muscular cells. To this latter are added a circular and in some places also a 
longitudinal layer of striped muscular fibres. 

The Nympile, Clitoris, and Vestibulum. 

All these parts are covered with a thick stratified pavement epithelium of the 
ordinary description. The mucous membrane underneath is a dense connective-tissue 
membrane, containing also elastic fibrils, and projecting into the epithelium as smaller 
or larger conical or cylindrical papillae containing loops of capillaries. 

The mucous membrane of the nymphae contains sebaceous glands conspicuous by 
their size, but no hairs. 

There is a superficial and a deep network of capillary blood-vessels in the mucous 
membrane of the nymphae, permeating a plexus of large veins, whose supporting tissue 
contains bundles of unstriped muscular cells, and hence this portion corresponds in 
structure to cavernous tissue (Gussenbaur). 

The corpora cavernosa clitoridis and the bulbi vestibuli coincide in structure to the 
cavernous bodies described of the analogous parts of the male (Gussenbaur). 

The genital end-bulbs and Pacinian corpuscles of the clitoris have been described 
in a former chapter. 

The glands of Bartholin are analogous to the glands of Cowper in the male. 
They are huge compound tubular mucous glands (see a former chapter). 

The connective-tissue separating the lobules contains unstriped muscular tissue. 
The alveoli or gland tubes are lined with a single layer of columnar mucous cells, 
imbricated with their outer pointed extremity (Langerhans). The ducts are lined with 
shorter or longer columnar epithelial cells. The chief duct possesses a special wall of 
connective-tissue and unstriped muscular cells. The stratified epithelium of the vestibu- 
lum is continued a short distance into the mouth of the chief duct. 

The Mammary Gland. 

As in other glands, so also here we distinguish tins, framework from the parenchyma ; 
the former is lamellar connective-tissue, subdividing the latter into the lobules and 
containing a small amount of elastic fibres ; in some cases, as in the rabbit, guinea pig, 
cow (Winkler, Kolessnikow), there are also small bundles of unstriped muscular cells to 
be met with. From the interlobular septa minute bundles of connective-tissue may 
be traced between the gland-alveoli. These bundles are well seen in the marginal parts 
of a lobule ; in the centre of this latter the alveoli are separated from one another 



FRAMEWORK OF MAMMARY GLAND. 30 1 

apparently only by the capillary blood-vessels. But there are everywhere branched 
nucleated connective-tissue corpuscles to be found between the alveoli ; according to 
Winkler also elastic fibrils, and in the rabbit, occasionally but not constantly, unstriped 
muscular cells. 

In the resting as well as in the secreting gland there are also migratory or lymph 
corpuscles to be found between the alveoli. They arc relatively more numerous in the 
former than in the latter; they vary in numbers in different glands and in different parts 
of the same gland. According to Creighton, in the resting gland, they are derived from 
the epithelium contained in the gland alveoli. The resting gland contains, in addition, 
in the connective-tissue surrounding its alveoli large granular yellow (pigmented) nu- 
cleated cells; similar cells are found also in the alveoli, and Creighton maintains that 
both are identical, being derived from the alveolar epithelium ; from the connective- 
tissue they find their way into the neighbouring lymphatic glands. The production of 
the small lymphoid and the large pigmented cells constitutes, according to Creighton, 
the principal function of the resting gland. 

The large ducts, passing from the lobules., possess a thick connective-tissue sheath 
and unstriped muscular cells. These latter are derived from the muscular bundles of 
which the skin of the nipple of the breast abounds. 

The parenchyma of the active mammary gland consists of the ducts and the alveoli. 
The membrana propria of the ducts is an endothelial membrane (Langerhans) ; it is lined 
with a single layer of columnar epithelial cells, each with an oval nucleus. On the nipple 
the rete Malpighii of the epidermis is continued a short distance into the mouth of the 
ducts. 

In the large lobular ducts the epithelial cells are short columnar or polyhedral. 
They give off the short terminal ductlets, lined with a single layer of flattened pavement 
cells, each with a spherical or slightly flattened nucleus. 

It is necessary to remember that also in this gland the height of the epithelial cells lining 
the ducts is dependent in a great measure on the state of contraction or distension (by secretion or 
otherwise) of the latter, for we find the epithelial cells in a large duct, if distended, less columnar 
than in a smaller branch, if contracted. 

Where the terminal ductlets join, so as to form a larger duct, the latter possesses a 
saccular dilatation. 

Each terminal ductlet takes up several alveoli ; these are longer or shorter wavy 
and convoluted tubes possessed of cylindrical or saccular lateral branchlets. Owing to 
the wavy and curved nature of the alveoli, each section made through the gland shows 
them cut in various directions, transversely, obliquely, or longitudinally. 

The diameter of the alveoli is larger than that of the ductlets. Each alveolus is 



V Y 2 



3 o2 ATLAS OF HISTOLOGY. 

limited by a membrana propria, lined with an epithelium ; in the centre of the alveolus 
is a distinct lumen. This latter varies in different alveoli of the same lobule; in the 
alveoli that are m a state of secretion it is a very conspicuous cavity, and is three and 
four times as large as in others, in which it is reduced to a minute canal. The state of 
secretion is indicated by its products (milk, albumen) being contained in the epithelial 
cells and in the lumen of the alveolus (see below). 

The membrana propria is a delicate transparent membrane, composed of a basket- 
shaped network of flattened branched nucleated cells (Langer, Kolessnikow). 

The epithelium lining the lumen is a single layer of granular-looking epithelial 
cells, each with a spherical nucleus. In the 'secreting' alveoli, that is in those with a 
large lumen, and containing the products of secretion, the epithelial cells are polyhedral 
or cubical, each with a spherical or slightly compressed nucleus. 

According" to Kolessnikow in some alveoli there is a second layer of small round cells to be 
found underneath the polyhedral cells lining the lumen ; a similar relation also exists, according to 
the same observer, in some of the ducts. 

In the alveoli with a minute lumen the epithelial cells are uniform and more or 
less columnar. But in the 'secreting' alveoli, some of the lining epithelial cells contain 
one or more larger or smaller milk globules ; the cells containing one big globule 
appear enlarged either towards the lumen, and are then columnar, or in the broad 
diameter, and are then cubical. 

The larger the globule, contained in the cell, the more distinctly is the nucleus 
pressed to the periphery, the cell substance being reduced to a protoplasmic mantle 
around the milk globule ; the appearance of such a cell is identical with that of a fat-cell 
filled with one large oil-globule (see Chapter VI.). 

The milk globules contained in the epithelial cells are each distinctly contained in 
a cavity (vacuole) of the latter, but they possess their own delicate albuminous mem- 
brane. Of precisely the same nature are the milk globules contained in the lumen of 
the alveolus, that is those that have been ejected from the epithelial cells, they possessing 
each their albuminous envelope, Ascherson's membrane (C. Schwalbe). This envelope 
can be recognised as a delicate membrane becoming faintly but distinctly stained in 
logwood. In a preparation of hardened gland treated with alcohol and oil of cloves, 
the fat of the milk globule having been dissolved, the albuminous envelope is alone left 
behind. 

The alveoli differ as regards the number of the epithelial cells containing milk 
globules, as well as regards the number of the latter excreted into the lumen of the 
alveolus. 








1* - 



II 








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p3 



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STRUCTURE OF MAMMARY GLAND. 303 

From all the appearances it seems then clear, that the production of the milk 
globules is similar to that of oil-globules in fat-cells, viz. it takes place within the cell 
substance, the smaller globules becoming gradually confluent into larger ones (Langer, 
Creighton, Winkler, Schmid, Kolessnikow, and others). 

It is most probable that the epithelial cells eject the milk globules produced in them 
without however becoming themselves (epithelial cells) destroyed (Langer). According 
to Schmid the epithelial cells, after having for some time secreted milk globules, undergo 
degeneration, and become replaced by new cells produced by the division of the other 
epithelial cells. 

The milk of a mammary gland in full secretion contains in a transparent homo- 
geneous interstitial fluid the milk globules. These are of very various sizes, and each 
consists, as already stated, of a thin albuminous envelope and a fat-globule. Very few 
remnants of broken-down cells and nuclei are found in the milk. 

In the colostrum there are contained numerous nucleated cells more or less filled 
with milk globules — the colostrum corpuscles. These exhibit amoeboid movement, and 
while moving may eject the milk globules (Strieker). 

During the transition of the resting gland into the state of lactation the alveoli filled 
with epithelial cells become greatly enlarged in numbers, their epithelium undergoing 
a corresponding multiplication ; the central cells of each alveolus become gradually filled 
with milk globules produced in them, and are carried away by the ducts as colostrum 
corpuscles (Hasse, Henle, Kolliker, Langer, Creighton, Buchholz, and others) ; the 
peripheral cells persist in the alveolus as the epithelium lining the membrana propria. 



The alveoli of the active gland are surrounded by a dense network of capillary 
blood-vessels, which for each lobule form a continuous system. 



In the interlobular connective-tissue He networks of lymphatic vessels (Langhans). 
The alveoli are surrounded by lymph spaces (Coyne) like the seminal tubes or the 
alveoli of the salivary glands (see former chapters). According to Kolessnikow they 
empty themselves into the interlobular lymphatic vessels. 

PLATE XL. 

Fig. I. From a section through a lobule of the mammary gland of the cat in the 
later stages of pregnancy. Magnifying power about 45. 

a, A lobular duct branching into four small ducts. The alveoli of the gland are 



3 o 4 ATLAS OF HISTOLOGY. 

indicated as spherical oval or oblong structures, many of them containing a coagulum 
stained brownish purple. 

b. The connective-tissue around the lobule. 

The epithelial cells lining the ducts as well as those of the alveoli are indicated by 

their nuclei only. 

Figs. II. and III. from the same gland as shown in fig. I., but under a much 

higher power, about 400. 

a. Alveoli in transverse section, their lining epithelium is seen in profile. It con- 
sists of a single layer of polyhedral or short columnar cells, each with a spherical or oval 
nucleus. Some of the cells contain a larger or smaller cavity, either filled with a milk 
globule stained purple, or empty, the milk globule having been discharged. In the 
cavity of the alveoli are seen such discharged milk globules of various sizes ; they are 
embedded in a finely granular matter, coagulated albumen. The purple staining of the 
milk globules is most probably due to their being each ensheathed in an albuminous 

envelope. 

b. The lining epithelium viewed from the surface. 

Fig. IV. From a vertical (longitudinal) section through the ovary of a half-grown 

cat ; magnifying power about 40. 

a. The albuginea ; the germinal epithelium covering it is not shown, owing to the 

low magnifying power. 

b. The cortical layer of small Grafian follicles. 

c. The next layer of middle-sized Grafian follicles. 

d. The deep layer of Grafian follicles, one containing three ova, each in a separate 
discus proligerus. 

e. The zona vasculosa of the hilum. 

Fig. V. A Grafian follicle of the layer c of the previous figure under a higher 

magnifying power, about 350. 

The Grafian follicle is surrounded by layers of the spindle-shaped cells of the 
stroma. A delicate membrana propria with staff-shaped nuclei forms the boundary of 
the follicle itself. The membrana propria is lined with the membrana granulosa, a single 
layer of beautiful columnar epithelial cells. The centre of the follicle is filled with the 
ovum, containing a large nucleus or germinal vesicle, in which is seen the germinal 
spot or nucleolus. The ovum is surrounded by a bright zona pellucida, here represented 
as a clear space, the outer surface of which is intimately connected with the interstitial 
substance between the cells of the granulosa. 

Fig. VI. From the same preparation as fig. IV., but under a higher power, about 350. 

1. Germinal epithelium of the surface. 



STRUCTURE OF GRAFIAN FOLLICLES. 305 

^ 2. Albuginea, compose! here of spindle-shaped cells, arranged as a -superficial longi- 
tudinal and a deep transverse layer. 

3. The groups of small Grafian follicles forming the cortical layer of Schron. 

Each of these follicles shows a distinct membrana propria lined with a layer of 
transparent flattened cells, membrana granulosa. The nucleus or germinal vesicle of 
the ovum contains a beautiful reticulum, not well shown in the fieure 

Fig. VII. From the layer d of the same specimen as in figure IV. Magnifying 
power about 350. 

a. Membrana propria and membrana granulosa (indicated by its nuclei) of a portion 
of a large Grafian follicle. 

b. The ovum in its discus proligerus. 

c. The stroma of spindle-shaped cells. 

d. A bundle of spindle-shaped cells cut transversely. 

e. Group of interstitial epithelial cells (see the text). 

Fig. VIII. A small Grafian follicle of layer c of figure IV., under a magnifying 
power of about 350. 

The membrana propria, the epithelium lining it, the zona pellucida, and the ovum 
are well shown. 

The germinal vesicle contains a well-developed reticulum, not distinctly shown in 
the figure. 

Fig. IX. Copied from Kolessnikow in ' Archiv fur mikroskopische Anatomie/ 
vol. xv. Plate xxv. 

From a section through the ovary of perca fluviatilis. 

a. The germinal epithelium. 

b. Two nests of epithelial cells, each with an ovum. 

The surrounding stroma is not represented here ; the nests are still in connection 
with the germinal epithelium of the surface (see the text). 

Fig. X. From a transverse section through the fundus uteri of a newborn child. 
Magnifying power about 40. 

a. Cavity of the uterus, lined with a layer of columnar epithelium ; the gland tubes 
embedded in the mucosa are seen cut in various directions. 

The figure represents not quite one half of the circumference of the cavity of the 
uterus. 

b. The mucosa ; owing to the low magnifying power only the nuclei of its cells are 
indicated here. 

c The inner muscular layer, composed of bundles, most of them cut obliquely 
because running in an oblique or more or less longitudinal direction. 



3o6 ATLAS OF HISTOLOGY. 

d. A broad middle layer of circular muscular bundles; between them are veins, of 
the cavernous body (see the text); the venous vessels are cut here in various directions ; 
between them are arteries and capillaries cut transversely. 

e. The outer layer, containing oblique and longitudinal muscular bundles, and be- 
tween them small veins, most of them cut transversely. 

Fig. XI. Portion of a venous sinus of the layer d of the preceding figure. 
Magnifying power about 90. 

s. Lumen of the venous vessel. 

m. Matrix composed of plexuses of bundles of unstriped muscular cells, and be- 
tween them connective-tissue ; the matrix projects into the vein in the shape of shorter 
or longer septa or trabecular 

c. Minute vessels, chiefly capillaries, rilled with, and greatly distended by, blood- 
discs stained brownish purple. 






307 



CHAPTER XXXIII. 

THE SKIN. 

The skin of man and mammals consists of the following parts : the epidermis, the 
corium or cutis with the papillae, and the subcutaneous tissue with the fat. 

The Epidermis. 

The different parts of the epidermis, viz. the rete or stratum Malpighii, the stratum 
of granular cells of Langerhans (stratum granulosum of Unna), the stratum lucidum, and 
the stratum corneum, have been mentioned in Chapter II. pp. 15 and 16. A few points 
only will be added here to the previous description. As regards the rete Malpighii — 
the term stratum Malpighii is preferable — it has been mentioned that the cells of the 
deepest layer are more or less columnar with oval nuclei, whereas those of the 
middle layers are polyhedral, with more or less spherical nuclei. The substance of 
the cells of the deepest layer, both in the skin of dark individuals and in such parts of 
the skin of man and mammals generally as are normally coloured (viz. the nipples, 
scrotum, and labia majora), contains a variable amount of brownish pigment granules. 

Both in the deepest and middle strata we meet with nuclei, whose outlines are 
more or less notched, and which therefore present a lobed, hourglass-shaped, or 
irregular appearance. This is probably due to the fact that during life the nuclei are 
possessed in a certain small degree of the power of spontaneous contraction (Flemming). 

The nucleus of some of the cells of the deepest layer contains within a distinct but 
delicate membrane a honeycombed reticulum, without any nucleolus. That of others 
does not possess any special limiting membrane, and includes a more or less dense con- 
volution of fibrils deeply staining in the different dyes. Then there are cells, whose 
nucleus has still further advanced towards division : the nucleus is larger, does not 
possess any membrane, and its fibrils become arranged as a rosette ; then they 
change into a star — Monaster, and later on into a double star — Dyaster. Now 
the cell itself becomes divided into two in a line separating the two stars of the 
dyaster. Each of these daughter stars is of course much smaller than the mother star 
preceding the stage of the dyaster. The daughter star changes into a Convolution ; this 
again changes into a nucleus, similar in size, shape, and appearance to the nucleus of the 
cells in the middle layer of the stratum Malpighii, being spherical, well-defined by a 

z z 



3 oS ATLAS OF HISTOLOGY. 

distinct membrane, and including a honeycombed reticulum with or without one or 
more thickenings — nucleoli. 

This indirect division of nuclei will be fully described in a future chapter, but it 
may be pointed out here that as a rule in the normal state only the cells of the deepest 
layer undergo the division, and that the cells derived from them pass on into the next 
layers. 

Occasionally, though very rarely, a nucleus of a cell above the deepest layer may 
be seen in one of the stages of indirect division. 

This mode of division has been observed in the nuclei of the deepest layer of cells 
of the epithelium of the cornea, of the skin and mucous membranes in the adult and 
embryo, under normal and abnormal conditions, in lower and higher vertebrates (Mayzel, 
Eberth, Flemming, Klein, Peremeschko). 

The cells of the deepest and middle layers are separated from one another by a clear 
interstitial cement-substance, which, as has been stated on former occasions, increases to 
a considerable extent under inflammatory conditions. The cell-substance is a dense 
reticulum, and hence presents the appearance of ' granular ' protoplasm, but contiguous 
cells remain connected by minute processes, i.e. of the prickle cells, described p. 16. 

Towards the surface of the stratum Malpighii the epithelial cells and their nuclei be- 
come more and more flattened, and gradually filled with peculiar granules. These granules 
are more or less discoid, and therefore appear rodlike in the profile view. They increase 
in size and numbers towards the surface of the stratum Malpighii, as has been stated 
p. 1 6. They stain a deep purplish blue in hematoxylin, and hence become very con- 
spicuous in preparations coloured with this dye. This section of the stratum Malpighii, 
viz. the cells containing the granules, represents the 'stratum of granular cells' (Langer- 
hans), ' stratum granulosum ' of Unna. The granules are neither protoplasm nor horny 
matter Keratin, like that of the cells of the stratum lucidum or stratum corneum, but 
are probably a transitional stage between the two. 

The stratum granulosum varies in thickness, in the different localities, like the epi- 
dermis as a whole ; in some places where the epidermis is very thick, as in the palm of the 
hand and foot, this layer is also well developed, consisting of three, four, and more layers 
of cells. In other places, as on the inner side of the arm and forearm, thigh, the cubital, 
popliteal, and similar regions, where the epidermis is very delicate, the stratum granulosum 
is only rudimentary. It is better developed at the mouth of the hair follicles and in their 
neighbourhood than in the parts between them, it is also well developed near the nails ; 
it is not found in the nail-bed (Heynold), but its absence is limited to the matrix of this 

(Hebra). 

In the stratum lucidum the scales are very closely pressed against one another, and 



STRUCTURE OF THE EPIDERMIS. 309 

each of them contains a rudiment of a staff-shaped or flattened nucleus. In many places 
longitudinal rows of what at first appear as bright granules can be distinguished in this 
stratum. These granules are, however, minute air-cavities between the layers of scales. 
After becoming confluent into clefts, a separation of these layers is effected, and a condi- 
tion is produced such as is found in the superficial section of the stratum corneum, viz. 
the layers of scales are more or less separated from one another by longer or shorter 
clefts. 

The stratum Malpighii rests on the papillary layer of the corium, and is sunk in 
between the papillae as the interpapillary processes ; the length of these varies in direct 
proportion to the height, the breadth in an inverse proportion to the closeness of position 
of the papillae. The constitution of the interpapillary processes differs from the other 
part of the stratum Malpighii in the following points : the vertical diameter, i.e. the 
thickness, of the stratum Malpighii is of course greater in the interpapillary processes than 
between them. This increase in thickness is due to the presence of a greater number of 
layers of what were previously described as the middle layers of polyhedral cells, with 
spherical nuclei ; the deepest cells of the interpapillary processes are placed vertically 
on the sides of the papillae of the corium and the grooves or pits between them ; those 
of the rest of the stratum Malpighii rest on the summits of the papillae. 

Occasionally the cells of the middle layers of the interpapillary processes are more 
or less elongated in a direction vertical to the surface ; hence they appear spindle-shaped, 
and their nuclei are then oval ; under these circumstances also the cells of the deepest layers 
are much drawn out, and are very thin, and spindle-shaped (Klein). Such a condition is 
due to the softness of the epithelial cells, and to their being consequently easily brought 
into those shapes by the shrinking of the skin during hardening or otherwise. 

The surface of the stratum Malpighii, including the stratum granulosum, pos- 
sesses a wavy outline where the stratum corneum and the stratum lucidum are elevated 
into permanent ridges with corresponding furrows between, as in the palm of the hand 
and on the fingers ; the breadth of the ridges is here about that of two or three papillae 
with their corresponding interpapillary processes taken together. 

The stratum Malpighii is firmly fixed on the surface of the corium by an albumi- 
nous cement identical with that which is found between the epithelial cells. The 
lower or deeper surface of the epithelial cells, that is the one resting on the corium, is in 
well-prepared specimens not quite flat, but indentated, and toothed ; when, as in the 
above-named condition of shrinking, the cells of the deeper layers are elongated to 
an abnormal extent, the appearance is produced as if they were continued by fine 
filamentous processes into the tissue of the papillae. The epithelial cells themselves are, 

however, not continued into the tissue of the papillae ; only the albuminous inter- 

z z 2 



, IO ATLAS OF HISTOLOGY. 

stitial or cement-substance between the epithelial cells can be traced into the similar 
substance containing the Iymph-canalicular system and separating the bundles of con- 
nective-tissue of the matrix of the papillae, a relation which has been minutely described on 
a former occasion, Chapter XXII. p. 175,111 connection with the epithelium of mucous 
membranes and the endothelium of serous membranes. And just as in the case of the 
mucous- and serous membranes, so also in the skin, the branched lymph-spaces and the 
connective-tissue corpuscles of the papilla; extend into, or rather are continuous with, 
branched lymph-spaces and their cells situated in the interstitial cement-substance of the 
stratum Malpighii ; here they may be seen to extend between the cells of the deeper and 
middle layers, their processes extending chiefly in a direction parallel to the surface ; hence 
they are better seen in horizontal sections through the stratum Malpighii ; their processes 
are then seen to lose themselves in the interstitial substance. These branched connective- 
tissue cells are very conspicuous, and easily perceived when they contain pigment gra- 
nules, as is the case in the pigmented parts of the skin of lower vertebrates and of 
mammals, as well as in the skin of dark individuals, and in the pigmented localities of the 
skin in general. These pigment granules are not to be confounded with the ones present 
in the substance of the deepest epithelial cells themselves. The intraepithelial branched 
nucleated connective-tissue cells have been mentioned in Chapter II. on p. 18; they are 
met with not only in all parts of the skin of man, mammals, and lower vertebrates, but 
also in all epithelium of mucous membranes and glands, as has been pointed out on many 

previous occasions. 

Biesiadecki saw them in the epidermis of the human skin, but took them to be 
leucocytes migrating into the epithelium to become there converted into epithelial cells. 
Langerhans found them in chloride of gold specimens, since they become deeply stained 
by this reagent, and chiefly for this reason they were by this observer and by Podkopaeff 
believed to be nerve terminations. 

Eberth and Eimer also saw them ; the latter found them to be very numerous 
in the nipple of the cow, but did not regard them as connected with nerve fibres. 

That they very probably are possessed of amoeboid movement is shown by : (1) the 
very great differences exhibited by their processes; in some instances they are possessed 
of short thick knoblike processes, in others of long filamentous branched ones ; (2) in the 
intraepithelial pigmented and unpigmented cells of the epithelium of the tail of the tadpole 
such movements, although slow, can be nevertheless distinctly observed. Similar move- 
ments have been observed in the intraepithelial branched cells of the cornea by v. 
Recklinghausen, Strieker, and others. 

Early in the fcetal state the branched connective-tissue cells of the skin and mucous 
membranes grow into the epidermis or epithelium respectively of the surface, and 



STRUCTURE OF THE CORIUM, 3 n 

thus represent the rudiments of the intraepithelial branched cells, as just described of 
the adult organs. 

The Corium. 

The boundary between the stratum Malpighii of the epidermis and the super- 
ficial part of the corium is represented by a fine but distinct membranous structure, 
basement membrane, which is very conspicuous in preparations stained with dyes. 
While in some instances it appears as a bright substance separating the deepest layer 
of epithelial ceils from the corium, in others it takes the staining very readily. But 
in all instances it appears to be merely the deepest portion of the epithelium and, In 
fact, is made up of the basis of the individual epithelial cells which has undergone a 
chemical and morphological alteration. The basement membrane is then a & direct 
product of the deepest layer of the epithelium, and its several constituent elements are 
comparable to the foot-plate (Fussplatte : Lett, Rollett, and others) of the deepest or 
columnar cells of stratified epithelium. 

The superficial part of the corium is raised as conical or cylindrical papilla*. These 
vary to a very great extent, both as regards their number and their size in different locali- 
ties, and at different points of the same locality. They are best developed in the corium 
of the human skin. The papillae are largest in the palm of the hand, on the volar side of 
the fingers, and the sole of the foot ; they are well shown on the scalp, lips of mouth, less 
so in the thin parts of the skin, as on the inside of the thigh and arm. In all instances, 
however, there exist the greatest differences as regards breadth and shape ; thus, for in- 
stance, in the scalp and other localities we meet with rudimentary thin and narrow papillae 
next to, or between well developed broad conical or cylindrical ones. In connection with 
this it is necessary to bear In mind that many papillae, being flattened from side to side, 
may in section present themselves either from their broad or narrow side. 

The matrix of the corium consists of bundles of fibrous connective tissue forming 
smaller or larger groups— trabecule, which cross each other and interlace in a complex 
manner, and so produce the feltlike density of the tissue of the skin. In the super- 
ficial parts of the corium, including the papillae, the bundles and their groups are small 
and their division and mode of interlacing is intricate ; in the deeper parts, or the sub- 
cutaneous tissue, the trabecular or groups of bundles are large ; they branch, re-unite, and 
cross each other in many directions. For this reason the superficial part of the corium 
contains much smaller and more numerous interfascicular spaces than the deeper parts. 
In the former there is all through the matrix a more or less uniform distribution of the 
hyaline interstitial interfascicular substance containing the lymph-canalicular system 
with its branched connective-tissue corpuscles, while in the latter there are larger and 



3 i2 ATLAS OF HISTOLOGY. 

more continuous interfascicular channels and spaces and the connective-tissue cor- 
puscles, as mentioned on a former occasion, form more continuous endotheloid 
membranes. 

All blood-vessels and nerve branches, ducts, glands, hairs, &c, are situated in the 
interfascicular spaces. 

The fixed connective-tissue corpuscles of the skin have been described in Chapter 

IV. pp. 28 and 29 ; they are in the superficial parts of the corium small transparent cells, 

composed of chief and secondary plates, all of them possessing filamentous processes ; 

in the subcutaneous tissue they are larger and less branched ; in some places they are 

even seen to form an endotheloid covering for the trabeculae. 

Each connective-tissue corpuscle includes an oval flattened nucleus, in which a 
fine reticulum can be made out. As regards the structure of these corpuscles refer to 
what has been said on p. 29. 

In the superficial parts of the corium, especially in the papillary body as well as in 
the deeper parts of the subcutaneous tissue containing the coiled tube of the sweat 
glands, we meet with a few migratory cells in the interfascicular spaces, besides the 
flattened connective-tissue corpuscles ; they are either small pale lymphoid corpuscles 
with one or two spherical nuclei, or they are two or three times larger, and possessed 
of coarse granules, which in some instances are brown pigment granules. 

The small pale corpuscles in the normal state are rare ; the corpuscles with 
coarse granules are occasionally tolerably numerous even in the normal state ; they 
move very slowly, possess a relatively large clear, spherical, or oval nucleus ; they 
correspond to Waldeyer s plasma cells. When unpigmented they assume in haematoxylin 
a deep purplish-blue colour, and hence become very conspicuous. 

Considerable numbers of elastic fibres are present in all parts of the connective-tissue 
matrix of the corium ; these fibres are much more numerous in the subcutaneous tissue 
than in the superficial part of the corium, and in the papillae they are scarce. They 
present themselves as fine and coarse elastic fibres, connected by lateral branches into a 
network. The direction of these fibres is always parallel to that of the trabeculae, to 
the surface of which they are closely attached. 

In most instances we find fine and coarse elastic fibres side by side in the same 
place, but there exist great differences in the skin in different localities and of different 
individuals, both in the quality of the fibres, viz. whether fine or coarse, as well as in 
their number. 

The deep section of the subcutaneous tissue contains smaller or larger groups of fat- 
cells, or a continuous thicker or thinner stratum of fat-cells arranged in lobules, the 
adipose stratum; between the lobules are thicker or thinner septa of fibrous connective 



ADIPOSE TISSUE OF SKIN. 



3*3 



tissue. Fine bundles of connective tissue and connective-tissue cells penetrate toother 
w.th the capillaries into the interior of the lobule between the fat-cells. 

As regards the structure, arrangement, and development of the fat-cells the 
reader is referred to Chapter VI. pp. 42 and 43 . , wish t0 add here ^ . as fa 
other parts of the body, as in the serous and mucous membranes, in the loose tissue 
connecting neighbouring organs, &c, so also in the skin the foetal fat tissue contains larger 
or smaller vascularis^ groups of cells which are in various stages of transformation into 
fat-cells, that is to say, whose protoplasm contains only a few or not even any oil dobules 
Gradually the o.l globules make their appearance in all cells, and their number in each 
cell becoming greater, they become confluent into one large oil globule which now is the 
most conspicuous part of the cell ; the protoplasm with the oval nucleus at one side forms 
a mantle around the oil globule, as has been described in Chapter VI. Now what I 
wish speoally to point out is, that even in the stage when few or no oil globules have 
appeared as yet in the above cells, these latter, being placed closely side by side give 
one the impression that they all are spherical or oval cells slightly pressed against one 
another and separated from place to place by a capillary blood-vessel only. In reality 
however, these cells are possessed of finer or broader processes, by which they 
anastomose with one another ; the number of these processes is not however very large. 

In a section through a hardened ganglion, the individual ganglion ceils appear to be without 
processes, although in reality they may be possessed of one, two, or more. 

At an early stage of development, when the lobule consists only of few cells, their nature 
of branched connective-tissue cells can be easier recognised. The very numerous 
lymphatics supplying the lobules of adipose tissue will be described below. 

The Sweat-glands. 

They are exceedingly numerous, and distributed uniformly in most regions of the skin 
Each sweat-gland is a simple tube composed of a coiled portion, or the gland proper' 
situated in the subcutaneous tissue, and a duct, passing in a more or less vertical or 
oblique direction and slightly wavy through the corium, and opening on the free surface 
of the epidermis. The coils in the same gland are separated by a small amount 
of connective tissue, containing the numerous capillary blood-vessels, lymphatics, and in 
some places also a few fat-cells. 

Beginning with the free opening, or the mouth, we trace the duct as a narrow canal,— 
at one place flattened and cleft-like, at another more cylindrical— and limited by a bright 
homogeneous membrane, through all the layers of the epidermis in a more or less zigzao- 
or spiral manner. The epidermic cells or scales respectively immediately surrounding the 



3 i 4 ATLAS OF HISTOLOGY, 

duct form a sort of concentric outer layer around the above bright membrane. It passes 
from the epidermis into the corium through an interpapillary process, this latter being 
continued, but decreasing in thickness, on the duct as its epithelium. 

The duct possesses also a continuation of the basement membrane mentioned 
above, and this is traceable over the whole length of the gland tube as the membrana 
propria. With nitrate of silver this membrane presents the appearance of an endothelial 
membrane (Czerny), but I doubt whether the individual scales possess a nucleus like 
true endothelial plates ; on the contrary, I am inclined to think that, just like the base- 
ment membrane, it is composed of the outer portion, the basis or foot-plate, of the 
epithelial cells next to it. 

The duct consists then of: (a) a narrow canal ; (b) a homogeneous bright membrane 
lining this ; (c) an epithelium which is composed of two or three layers of small 
polyhedral epithelial cells each with a spherical or oval nucleus, and (d) outside this a 
delicate membrana propria. 

The lumen or canal of the duct is distinct, in most places cylindrical, and therefore 
circular in transverse section. Whether the bright membrane lining this is homogeneous 
or possessed of flattened nuclei it is difficult to ascertain ; in some places, when looked 
at in profile, it certainly seems as if there were present in it at rare intervals staff-shaped 
nuclei, The lining membrane stains well in carmine. When it reaches the sub- 
cutaneous tissue, the duct becomes suddenly many times coiled up. 

The first or proximal section, about one-third or one-fourth of the coiled tube, retains 
the same structure as the duct, and differs from it in the fact that it is coiled up and 
that its lumen is somewhat larger. The remainder, or the distal part of the coiled 
tube, is of a different nature, inasmuch as the membrane lining the lumen is reduced to 
a very delicate film, and the epithelium, which hitherto consisted of two or three layers 
of small polyhedral cells each with a spherical or oval nucleus, is replaced by a single 
layer of columnar longitudinally striated cells, each with a spherical nucleus in the outer 
part of the cell. The membrana propria of this section is however much thicker than 
in the former, and contains on its inner surface, that is, the one next the epithelial cells, 
a single and continuous layer of very slender unstriped muscle cells arranged parallel 
to the lono- axis of the tube. In some glands this muscle layer is more conspicuous 
than in others ; in some it is rudimentary, not being quite a continuous layer. As 
Ranvier pointed out, in the fcetus this layer of muscle cells is represented by a layer of cells 
identical in aspect and origin with the epithelial cells, so that in the fcetal gland there are 
two layers of epithelial cells, one, the inner one, which gives origin to the permanent epi- 
thelium, while the other is changed into the unstriped muscle cells. 

As in other glands, so also here the state of contraction and that of distension by 



STRUCTURE OF SWEAT-GLANDS. 3I5 

the secretion has an important effect on the diameter of the lumen and the length of 
the lining epithelial cells. The smaller the lumen, the longer and thinner the epithelial 
cells ; the more distended the former the shorter the latter. This distal portion of the 
coiled tube is then, even under a lower power, conspicuously different from the prox- 
imal, being thicker and more transparent. 

In some localities, as in the scalp, palm of hand, and sole of foot, and especially the 
axilla, the scrotum, nipple, and labia majora, the distal portion of the coiled tube becomes 
greatly developed : being much longer, broader, and its muscle coat more conspicuous 
than in other localities. 

In the sweat-glands of some of the domestic animals, as in the dog, pig, sheep, the 
gland consists of a long, more or less straight, narrow duct and a wavy or more or less 
convoluted tube; the former opens generally into the neck of a hair-follicle ; it has a 
cylindrical lumen lined with a delicate membrane, which in some instances (dog) appears 
distinctly composed of nucleated scales. A single layer of short polyhedral cells, each 
with a spherical or oval nucleus, is found outside this membrane; the boundary is 
formed by a membrana propria. The duct passes suddenly into a broad tube (Stirling) 
which corresponds to the distal part of the coiled tube of the human sweat-o-land. The 
longitudinal muscle coat is everywhere strikingly developed, and lies between the epi- 
thelium and the membrana propria. The epithelium is a single layer of shorter or 
longer columnar, transparent, or longitudinally and finely striated cells. The limiting 
membrana propria is generally thick, much thicker than in the human sweat-glands. 
The epithelial cells lining the duct do not appear continuous with those of the rest of 
the tube, and seem to commence suddenly at the end of the duct. 

In all sweat-glands connective-tissue cells of the surrounding tissue may be seen to 
extend through the wall, and they may be found as small-branched nucleated corpuscles 
between the epithelial cells, as has been noticed of other glands in a former chapter. 

The ceruminous glands of the external ear-passage are situated in the subcutaneous 
tissue ; they are similar in structure to the sweat-glands of other parts, but the 
coiled tube corresponds in structure to the distal part only of the ordinary sweat-gland. 
The tube is large and is lined with a single layer of columnar cells, each of which pos- 
sesses a clump of pigment granules in the inner part ; a spherical nucleus is situated in 
the outer portion of the cell ; between this layer of epithelial cells and the distinct 
homogeneous limiting membrana propria is a continuous layer of unstriped muscle 
cells (Sangster). 

3 a 



3l6 ATLAS OF HISTOLOGY. 

The human anus is surrounded by an elliptical zone containing large coiled gland 
tubes, the circumanal glands of A. Gay. Each of these glands corresponds to a huge 
sweat-gland; it is composed of a duct and of the coiled tube which in its structure coin- 
cides with the distal part of the ordinary sweat-gland, viz. its epithelium is a single layer 
of transparent columnar cells; outside these is a continuous longitudinal layer of unstriped 
muscle cells, and outside these is the thick homogeneous limiting membrana propria. 

The peculiar sweat-glands situated in the eyelid, and known as the glands of Moll, 
will be described in connection with the eyelid. 

The presence of a longitudinal layer of unstriped muscle cells was first pointed out 
by Kolliker in the sweat-glands of the axilla, of the root of penis, and of the nipple. 
Krause and Heynold found them in all glands. 

That the muscle coat is between the homogeneous membrana propria was pointed 
out by Kolliker, myself, Sangster, and Hesse; for the glands of Moll the same was 
pointed out by Sattler. 

That the duct of the sweat-gland possesses, next to the lumen, a homogeneous 
membrane, a sort of cuticle, was correctly described by Heynold and also by 
Horschelmann ; with the latter I find it also in the proximal part of the coiled tube. 

That the coiled tube of the sweat-gland of man, with the exception of the cerumi- 
nous and circumanal glands, consists of a smaller proximal and a longer and larger distal 
part has been indicated already by Heynold and Horschelmann, both of whom stated 
that the duct contributes to the formation of the coiled tube. 

According to Hesse the ducts of the sweat-glands of the axilla and anus often open 
into the mouth of a hair follicle. 

Renaut pointed out a difference of aspect during rest and secretion in the epithelial 
cells of the sweat-glands of the horse, being transparent with peripherally placed nucleus 
before, granular with central nucleus immediately after, secretion. 

The sweat glands in the earliest stages are solid knob-like projections of the stratum 
Malpighii into the tissue of the corium ; they appear closely at the side of the hairs but 
much later than the latter, about the fifth month in the human foetus. They are, like the 
stratum Malpighii of the foetus, composed of polyhedral small cells, each with a spherical 
nucleus. The cells of the outermost layer, however, like those of the deep layer of the 
stratum Malpighii, are slightly elongated, columnar. These rudiments grow through 
the corium into the subcutaneous tissue, where they begin to coil. 

Very soon, however, before they have grown far into the depth of the corium, the 
epithelium of the duct shows a distinction into central and marginal cells, the former being 
much elongated and spindle-shaped. It is quite possible that these elongated cells are 



STRUCTURE OF HAIR-FOLLICLES. 3 i 7 

the cells from which the inner membrane lining the canal is derived. Of a canal there 
is little to be seen in the duct at birth, whereas even at this period the coiled tube shows 
already a distinct though small lumen. At birth the distal part of the coiled tube possesses 
a well-marked muscle coat, and its epithelium consists of a layer of columnar cells. 

The Hair-follicle, the Hair, and the Sebaceous Gland. 

In each hair-follicle we distinguish the mouth, the neck, the main portion or the 
body, and finally the bulbous extremity. The mouth is a funnel-shaped opening on the 
free surface, and the neck lies in the level of the papillary layer of the corium. 

The direction of the hair-follicle, and of course also of the hair occupying its axis, 
in the skin, is always an oblique one, the distal or bulbous extremity forming in most 
cases a straight line with the rest, but sometimes, as in the case of the hairs of the lips 
of the mouth, it is slightly curved. According to Stewart this is the normal state with 
the hairs of the scalp of the negro. 

The distal extremities of the well-developed hair-follicles extend into the septa of 
the adipose tissue ; they extend therefore much deeper into the subcutaneous tissue 
than the sweat-glands, whose coiled tube, as mentioned previously, reaches no farther 
than the superficial section of the subcutaneous tissue. 

The hair-follicles in the scalp are situated in groups of three or four, and the indi- 
vidual hair-follicles of these groups are of various thicknesses. 

The size and especially the length of the hair-follicles vary greatly in the different 
localities. 

Each hair-follicle consists of the vascular hair-sac, the papilla and the outer root 
sheath. 

The hair-sac is composed of an outer longitudinal and an inner transverse coat. It 
appears as if it were part of the surrounding tissue of the corium, with which it is inti- 
mately connected, but it must be regarded as altogether an organ independent of this 
latter. It is in reality a continuation of the papillary layer of the corium, which it re- 
sembles in being supplied with a network of capillaries and, as will be pointed out 
below, from which it developes in the fcetus ; it is continuous with the connective 
tissue of the septa which penetrate between the lobules of the adipose tissue. 

The bundles of the outer coat are longitudinally arranged, while those of the inner 
are more oblique or transverse. In many places only the outer or longitudinal coat 
is distinct; in some, however, especially near the distal extremity or the bulb, a rudi- 
ment of transverse thin bundles can also be made out. On the inner surface of the 
transverse coat may be seen a continuous layer of relatively short and broad unstriped 

3 A 2 



3*8 



ATLAS OF HISTOLOGY. 



muscle cells, each with a relatively long staff-shaped nucleus. The muscle cells arc 
situated transversely to the long axis of the hair, and are best seen in the distal third or 
fourth of the hair-follicle, that is to say in the bulbous part. 

At the rounded extremity of the hair-follicle the tissue of the hair-sac, exclusive of 
the muscular layer, is pushed in as the club-shaped, pear-shaped, or spherical papilla into 
the similarly shaped excavation of the bulbous extremity of the hair. The tissue of the 
papilla is composed of a hyaline matrix in which few thin fibrous bundles and numerous 
branched connective-tissue cells may be met with besides capillary blood-vessels and 

nerve fibres. 

The hair-sac, inclusive of the papilla, is separated from the next following or inner 
stratum of the hair-follicle by a glassy hyaline basement membrane ; this is thin near 
the mouth of the hair-follicle, increases in thickness towards the distal part, and reaches 
its neatest thickness near the bulbous extremity ; it becomes again thinner as it 
approaches the papilla, and over this it is only a very delicate membrane. 

This glassy membrane of the hair-follicle is a direct continuation of the basement 
membrane of the corium, and like this is derived from the deep portion of the epithelial 
cells next to it : in the case of the basement membrane of the corium, the deep layer 
of the stratum Malpighii ; in that of the hair-follicle, the outer layer of the outer root- 
sheath. As will be pointed out presently, this is a direct continuation of the epidermis 
of the surface, and so may be regarded as the epithelium of the hair-follicle. 

At the mouth and neck of the hair-follicle the outer root-sheath is identical with 
the epidermis, and therefore includes all its layers (v. Ebner), viz. the stratum 
corneum, the stratum lucidum, the stratum granulosum, which is specially well marked 
here, and the stratum Malpighii ; in the rest of the hair-follicle the outer root-sheath 
is represented by cell-layers identical with the stratum Malpighii only. Consequently, 
like this latter, it consists of a marginal layer of columnar cells, each with an oblong 
nucleus, and several layers of polyhedral cells, each with a spherical nucleus. Nearest 
the central axis of the hair-follicle, that is towards the hair itself, the cells are much 
flattened and possessed of flattened oval nuclei. In some cases the cells of the 
marginal and middle layer of the external root-sheath are prickle cells, like those of the 
stratum Malpighii. The outer root-sheath varies in thickness in different parts of the 
hair-follicle ; it reaches its greatest thickness about the middle portion of the follicle. 
Near the extremity it becomes suddenly reduced to a single layer of flattened cells, and 
then passes over the papilla, the cells, however, changing from flattened into columnar 
ones. Over the papilla they merge insensibly into the mass of polyhedral cells forming 
the hair-bulb itself. 

Just as we mentioned of the stratum Malpighii and the sweat-glands, so also in the 



STRUCTURE OF HAIR. 319 

external root-sheath and its continuation over the papilla, we meet with branched con- 
nective-tissue cells, in their respective lymph- canalicular system, penetrating- from the 
hair-sac, or the tissue of the papilla respectively, between the cells of the outer root 
sheath ; here their processes are lost in the interstitial or cement-substance. 

This relation is very distinct in the foetal as well as in the adult hair-follicles. In 
the foetal skin of many mammals these interstitial branched cells of the outer root-sheath 
are pigmented. 

In sections showing the outer root-sheath, or portions of it, in a bird's-eye view, the 
richness of these intraepithelial branched cells is very marked. In those parts where 
the glassy membrane separating the external root-sheath from the hair-sac is very 
well developed and thick, the branched lymph-canalicular system containing these 
branched cells and extending from the connective-tissue of the hair-sac through the 
glassy membrane into the interstitial substance, i.e. between the cells of the outer root- 
sheath, is easily followed. 

Each hair is divided into the root embedded in the hair-follicle, the shaft, freely 
projecting over the surface of the skin, and terminating in an attenuated free extremity, 
and the bulb or the thickened distal extremity, inflected over and fixed on the papilla. 
The root of the hair consists of the substance of the hair, the cuticle, and the hair 
sheath, or the inner root sheath. 

The substance of the hair is composed of very long filamentous, spindle-shaped, 
or narrow and long flat horny scales, which, when treated with caustic alkalies or 
strong acids, can be isolated from one another. They are then seen to contain a linear 
remnant of a nucleus. The hair scales are arranged in groups, which in a transverse 
section through the hair appear as small polyhedral zones ; in strongly pigmented 
hairs the outlines of these zones are unpigmented. Between the hair scales are found 
the finest air bubbles, as in white hairs, or rows of minute pigment granules, generally 
absent in white hair, but present in various quantities and shades of colour in coloured hair. 

These pigment granules, when not abundant, are not contained in the hair scales 
themselves, but in the interstitial substance separating them, as is more easily ascertained 
at the bulb. Besides these pigment granules there is diffuse pigment contained in the 
hair scales. But it is chiefly the granules situated in the hair substance which deter- 
mine the colour of the hair (Pincus, Boccardi). The different coloration in one and the 
same grey hair is due to the pigment granules being present in smaller numbers in some 
places than in others (Pincus). The hair becomes grey if the pigment situated between 
the cells of the bulb is not reproduced, as it then becomes gradually exhausted 
(Boccardi and Arena). 



320 ATLAS OF HISTOLOGY. 

In many instances the central part of the hair proper is occupied, not by the elongated 
filamentous hair-scales, but by one, or two, or three rows of small polyhedral or cubical 
cells, each with a spherical nucleus. Their nature and shape can be easily ascertained 
by treating the hair with strong alkalies or strong acids. This is the marrow of the 
hair. Its cells are in the natural state filled with minute air-globules, hence appear 
black in transmitted light. After hardening the skin, the marrow can be distinguished 
in transverse section through the hair as a more transparent central portion without 
any pigment granules. 

The surface of the hair is covered with the cuticle ; this is a single layer of minute 
horny scales without any nucleus, slightly elongated, and arranged transversely over the 
substance of the hair. They are slightly imbricated with their margins, and hence, 
when the cuticle is seen in profile, form a toothed or zigzag line like the teeth 
of a saw. 

Next to the cuticle of the hair lies the inner root-sheath. This is composed 
of three different layers : a cuticle, an inner or Hitxieys layer, and an outer or Henles 
layer. The cuticle presents itself as a very delicate film, and is distinct only 
when the hair is treated with strong alkalies or acids ; it appears then as an almost 
homogeneous membrane, composed of scales imbricated with their margins-and without 
nuclei. The inner, or Huxley's layer, is a single or occasionally double layer of cubical 
or oblong homogeneous cells, each with a small remnant of a nucleus ; this is not, how- 
ever, always distinct, especially not in the hair of some animals (pig, dog). The outer, 
or Henle s layer, on the other hand, consists of small, polyhedral, glassy-looking cells, 
ordinarily without a nucleus ; in some animals (pig) they show, however, a staff-shaped 
nucleus. 

In sections through hardened specimens showing the root of the hair in longitudinal 
view, the above three layers of the inner root-sheath appear as one thick glassy mem- 
brane on each side of the cuticle of the hair, and in it there is but a faint indication of a 
division into its three layers. 

The inner root-sheath lies close to the hair proper and reaches to near the neck of 
the follicle, where it terminates abruptly. Between the inner and outer root-sheath 
there is a delicate membrane to be noticed in some hairs, but this is probably only the 
most superficial layer of the flattened scales of the outer root-sheath. 

The shaft is identical in structure with the root, except that it does not possess a 
root-sheath and that its substance is harder and dryer. 

Both the root of the hair and the inner root-sheath form one organ and pass into, 
or rather develop from, the mass of cells forming the hair bulb. This is a mass of 
polyhedral cells covering the papilla, each with a spherical nucleus ; those immediately 



RELATION OF BULB TO ROOT OF HAIR. 321 

over the papilla are more or less columnar, and represent, as mentioned above, a direct 
continuation of the marginal layer of cells of the outer root-sheath. 

How are the cells constituting the bulb continuous with, or, in other words, how 
are they transformed into the different parts of the hair and inner root-sheath ? 

a) At the bulb the polyhedral cells immediately around the papilla in the direction 
of the axis of the hair pass into, at first slightly then more distinctly, elongated and 
spindle-shaped cells, whose nuclei elongate in proportion as the cells become drawn 
out ; from these we gradually pass to the very long cells with staff-shaped nuclei 
that form the substance of the hair-root Where there is a marrow, the polyhedral cells 
of this latter form an uninterrupted continuity with similar cells in the centre over the 
papilla. 

6) The polyhedral cells next to the axial cells forming the hair-substance pass, 
in a single layer, into the cuticle of the hair. 

c) The next outer layer of polyhedral cells of the bulb is continuous with the 
membrane separating the cuticle of the hair from Huxley's layer. 

d) The one or two layers of cells following next pass into the layer of Huxley; 
and finally 

e) The outermost layer or two into the layer of Henle. 

In all these different layers, as we pass from the bulb on to the root of the hair 
we see the small protoplasmic polyhedral cells of the bulb becoming gradually flattened 
and transformed into horny scales ; their nucleus loses its spherical shape, becomes 
more staff-shaped, and ultimately altogether disappears, except in the cells of Huxley's 
layer as mentioned above. 

Both in the foetal, young, and adult hair, but more easily in the former, a 
special layer of cells (/), beginning at the bulb end of the root and extending on the 
lower third of this latter, can be distinguished between the above layers b and c, that is, 
between the cuticle of the hair and that of the inner root-sheath. This layer,/ consists 
of spindle-shaped cells each with a relatively long staff-shaped nucleus ; the cells and 
their nuclei are placed transversely across the long axis of the hair, and resemble in all 
respects unstriped muscle cells just like those of the inner coat of the hair-sac. When 
focussing on this part of the root of the hair, when this has been cut in a longitudinal 
direction, the above layer of transversely arranged cells appears around the hair 
exactly like the transverse muscle cells in a small artery. They stain differently from 
the other cells of the root, and are conspicuous amongst them ; they diminish in size as 
we ascend the root, and finally disappear altogether. They are not continuous with 
either the cuticle of the hair or any part of the inner root-sheath. 

The bulb contains a quantity of pigment granules varying in amount and shade of 



322 



ATLAS OF HISTOLOGY. 



colour according to the colour of the hair; but this pigment is present only in the part 
around the papilla, that is in the part which is continuous with the substance of the hair. 
When not very abundant, these pigment granules are contained in the branched cells 
of the interstitial substance only, as stated above, and by them the epithelial cells of the 
bulb are finely mapped out. When very abundant, however, they also appear contained 
in the substance of the epithelial cells themselves. 

Passing from the bulb on to the hair root, the cells, as we have seen, become elong- 
ated, and the configuration of their interstitial substance changes accordingly, and con- 
sequently the arrangement of the pigment becomes of an elongated nature, always 
remaining between the cells of the hair substance, as mentioned on a former page. 

The hair-follicles and hairs of animals are in most respects identical in structure 
with those of man, the pigment in the interstitial substance of the cells constituting the 
hair substance and its bulb being in coloured hairs very great. The tactile hairs in 
the snout, eyelids, face, fingers, &c, of many mammals are distinguished from the ordi- 
nary hairs by the presence of an erectile tissue, viz. blood-sinuses surrounded by unstriped 
muscle tissue, chiefly around the neck of the hair-follicle. 



The Sebaceous Gland. 

Each hair-follicle is connected with one or two sebaceous glands opening into the 
neck of the former. The epithelium of the outer root-sheath, and the homogeneous 
basement membrane outside it, are connected with the epithelium and membrana propria 
respectively of the duct, passing sideways in an oblique direction into the corium, 
but always remaining more or less close to the hair-follicle. 

In the large sebaceous glands the duct after a short distance branches into three or 
more short smaller ducts, each of which passes into a single or double, longer or shorter 
flask-shaped or saccular, pear-shaped or tubular alveolus, with a csecal extremity. 

The alveoli, as a rule, never reach so deep as the coiled tube of sweat-glands, 
being situated in the middle portion of the corium. 

The ducts are lined with stratified epithelium similar to the outer root-sheath ; 
but it, viz. the epithelium, is reduced to one or two layers of small cells, while the lumen 
is filled with remnants of the altered gland cells constituting the elements of the 

sebum. 

In the alveoli we find a marginal layer of small polyhedral granular-looking 
epithelial cells, each with a spherical nucleus ; these cells are continuous with the 
marginal layer of cells of the duct, while the rest of each alveolus is occupied by polyhedral 
cells, whose intracellular network is filled with fat globules ; when these are dissolved 



STRUCTURE OF SEBACEOUS GLANDS. 323 

away by reagents the above network becomes very conspicuous. The cells increase in 
size from the marginal layer towards the centre of the alveolus. 

The marginal layer of cells by division produces new cells ; these are gradually 
pushed on towards the centre of the alveolus, the spaces of the intracellular network 
becommg at the same time distended by, and filled with, fat globules, and hence 
the cells gradually become larger. The nucleus is spherical, single, and situated about 
the middle of the cell. 

Ultimately the cells are shifted into the duct ; here they do not possess any nucleus, 
and having altogether lost their regular shape and outline, shrink and collapse into 
amorphous remnants, their fatty contents having previously become free. 

The sebaceous glands vary greatly in size in different localities ; they are generally 
larger where the hair-follicles are larger. In the foetus and young child the sebaceous 
gland and its duct are comparatively much larger than the hair-follicle, and hence the 
appearance is produced as if the hair were situated in, that is, as if it were part of the 
duct of the sebaceous gland. 

As a rule, the duct of the sebaceous gland opens into the neck of the hair-follicle, 
but in certain localities, as in the labia pudendi majora, scrotum, nostrils, we also find 
some sebaceous glands opening with their duct free on the surface of the epidermis ; 
in these cases the sebaceous glands are of a very large size. This is the case also with 
the large sebaceous glands, or Tyson's glands, on the prepuce and the corona of 
the glans penis. There are no sebaceous glands on the volar side of the hand and the 
foot, the dorsal side of the last phalanx of the digits, and the glans penis. Sebaceous 
glands of a very large size, both as regards the number and length of the ducts and 
alveoli, are met with in the skin of the sheep. 



The Muscle of the Hair. 

The arrector pili is composed of unstriped muscle cells ; in the hair of the adult 
human skin, especially in the scalp, the muscle attains a very great thickness, being 
composed of several bundles separated from one another by the connective tissue of the 
corium ; but these bundles are always connected with one another so as to form a 
plexus. The muscle begins at the hair-sac, a short distance above the bulbous portion 
of the hair-follicle. 

The muscle cells can be traced very closely to the glassy limiting membrane 
between the hair-sac and the outer root sheath, and they are continuous with the 
transverse muscle cells belonging to the inner coat of the hair-sac. The muscle ascends 
in an oblique direction through the corium towards the surface of this latter, generally 

3 b 



ATLAS OF HISTOLOGY. 



o 



so as to form a sharp angle with the hair axis ; it grasps the bottom of the sebaceous 
oland like a sling (Hesse), and when arrived at the surface of the conum its bundles 
branch and anastomose so as to form a plexus more or less horizontally placed. The 
bundles, after a shorter or longer course, lose themselves in the connective tissue of the 
papillary layer of the corium. The arrector pill of clog's hairs includes very many elastic 

fibrils (Stirling). 

At the point of insertion of the arrector pill into the hair-sac we often see the outer 
root sheath forming one or two smaller or larger projections. Similar but more finger- 
shaped and more numerous projections are found in those hairs, both of children and 

adults, that are to be shed. 

These projections indicate probably an active growth of the cells of the outer root 
sheath, and are due to the permanent irritation caused by the (pulling) action of the 

arrector pili. 

In the hair- follicles in which the old hair is to be replaced by a new one, we com- 
monly see one or two, or even three, such projections of the outer root sheath, each 
transformed into a cyst ; this contains a large transparent cavity, and its wall is made up 
of several cell layers, which by a solid thinner or thicker neck are connected with the 
cells of the outer root sheath. Derby and Gay found such cystic outgrowths under 
pathological conditions, but Esoff has shown that they are of normal occurrence in the 

hairs that are to be shed. 

The corium of the scrotum, nipple of the breast, labia pudendi majora, penis, 
contains independent bundles of unstriped muscle cells; these bundles are of various 
thicknesses and run in an oblique or horizontal direction in all layers of the skin, but are 
always connected into plexuses, as has been long ago pointed out by Kolliker, to whose 
observations we owe most of our knowledge of the muscles present in the skin of man. 

Striped muscle fibres in bundles enter the skin of the face from outside and 
terminate in the papillary layer of the corium. 

Growth, development and new formation of the hair and hair-follicle. 

The hair grows at the bulb, owing to the multiplication of its protoplasmic cells, 
chiefly those immediately surrounding the papilla. 

The oldest cells, viz. those furthest from the papilla?, become gradually elongated, 
and are then to be regarded already as part of the substance of the hair. The layer 
of cells containing the elements of the cuticle of the hair keeps pace with the 
substance of the hair. But the cells forming the inner root sheath do not grow at the 
same rate, being very much slower ; this latter keeps the same pace as the external 
root sheath of the hair-follicle. 



DEVELOPMENT OF THE HAIR-FOLLICLE. 325 

The rudiments of the first hairs appear in the human foetus about the end of the 
third month, and, just as in mammals, are at first solid knoblike outgrowths of the 
stratum Malpighii into the corium (Remak, Kollikor), especially of the deepest layer of 
columnar cells. In some instances the corium shows a slight elevation preceding the 
formation of the rudiment of the hair (Reissner, Gotte) ; but this is absent in many 
instances (Feiertag). 

The rudiment of the hair rapidly elongating becomes cylindrical, and we notice in 
it the following different elements : the majority of the cells are small and poly- 
hedral, in the marginal layer they are hexagonal or slightly columnar ; the former 
possess a spherical, the latter an oval nucleus ; the cells and their nuclei in the axial 
portion of the hair-rudiment are slightly flattened. There is a distinct limiting mem- 
brane between the marginal layer of cells and the surrounding tissue ; this membrane 
represents the rudiment of the glassy basement membrane. Each of the hair- 
rudiments is from the earliest time surrounded by a thick layer of a tissue altogether 
different from the rest of the corium and representing the rudiment of the hair-sac & ; it is 
well marked off from the corium, is composed of a network of flattened, spindle-shaped 
or branched cells, and stains as a whole better than the rest of the corium ; although 
relatively very bulky, it nevertheless can be traced directly to a thin layer similarly 
constituted and situated immediately underneath the epithelium of the surface, that is 
to say, a layer which gives origin to the papillary body of the corium. 

On a previous page we have pointed out that a definite distinction must be drawn 
between the hair-sac and the surrounding corium, and we see this is borne out by the 
development. The branched cells of the rudiment of the hair-sac soon make their way 
into the above solid cylindrical hair-rudiment, and thus give origin to the branched 
nucleated cells that we described as present in the adult state between the cells of the 
outer root sheath. 

The tissue of the hair-sac grows much more rapidly than the hair-rudiment, and 
having closed round the deep extremity of the latter, grows now against it as the 
papilla, and thus produces the inflection and enlargement of the bulb. Henceforth 
the multiplication of the cells at the bulb naturally leads to the new offsprings being 
pushed up in the axis of the hair-rudiment towards the surface, and becoming 
elongated constitute the elements of the hair-substance, its cuticle and inner root sheath ; 
the cells of the primary solid cylinder represent the rudiment of the cells of the outer 
root sheath only. The gradual conversion of the cells of the bulb into the spindle- 
shaped horny scales of the substance of the hair, the differentiation at the bulb of the 
cell-layers, and their conversion into the cuticle of the hair and the inner root sheath 
are easily understood from the description given above of these parts of the adult hair. 



3 B 2 



326 ATLAS OF HISTOLOGY, 

One of the latest parts to appear is the mouth of the hair-follicle. The hair itself 
and the inner root sheath, having reached the stratum corneum of the surface, for a 
short time continue to grow underneath it for a considerable distance in a hori- 
zontal or slightly oblique direction; ultimately, however, the stratum corneum is 
broken, and the mouth of the follicle having thus been established, the hair henceforth 
grows beyond the Tree surface, loosing the adhering parts of the inner root sheath 
from the neck outwards. 

As soon as the rudiment of the papilla makes its appearance, the hair-follicle, 
then still a solid cylindrical mass of cells, pushes out, near its connection with the 
surface epithelium, a small knob composed of the same polyhedral cells as the hair- 
follicle ; this knob gradually elongates, divides at its extremity, and its branches are 
converted into the alveoli of the sebaceous gland. The duct is therefore an outgrowth 
of the neck of the hair-follicle. 

According to Lowe, the correctness of whose statements must be questioned, the marginal 
layer of epithelial cells lining'the limiting membrana propria of the alveoli of the sebaceous gland 
is alone derived from the deepest layer of columnar cells of the epidermis, while the rest of the 
gland cells are offsprings of the stratum corneum. 

The fully developed fatal hair (lanugo) is very thin, its follicle and papilla do not 
reach into the subcutaneous tissue. It becomes replaced in many localities soon after 
birth by a much coarser hair, whose follicle and papilla pass down into the depth of 
the subcutaneous tissue. This new hair is produced from the outer root sheath of 
the primary hair-follicle (Kolliker), as will be presently described. 

Every hair in the young child, as well as in the adult, sooner or later undergoes a 
peculiar change, which leads to the formation of Henle s hair knob, or the intercalated 
hair (Schalthaar) of Gotte, or the bedhair (Beethaar) of Unna, differing in several im- 
portant respects from the normal or perfect hair, as described on a former page, and 
called by Unna the'papillary hair. The mode of change of the latter into the bedhair is 
the following : the cells of the bulb over the papilla cease to multiply, and consequently 
the hair and its inner root sheath stop growing ; first the inner, then the outer root 
sheath atrophy; but the root of the hair remains connected with the papilla for some 
time by a thin streak of cells ; ultimately also this disappears. This process of atrophy 
extends up to near the point where the arrector pili is attached to the hair-sac ; here the 
external root sheath becomes conspicuously enlarged and the hair root terminates in it 
with Henle's ( hair knob,' being an enlarged broomlike extremity, which with its fibrous 
horny elements branches out amongst the adjacent cells of the outer root sheath. The 
inner root sheath is wanting just at the extremity, but is met with at a short distance 
higher up. The hair continues to grow at its knob at the expense of the adjacent 



NEW FORMATION OF THE HAIR. 32? 

flattened cells of the outer root sheath, and in this condition, viz. as a bedhair, it may 
retain its position and existence for a considerable time. In many instances it is, 
however, eliminated spontaneously or by the growth of a new hair produced from the 
cells of its (viz. the bedhair's) outer root sheath. 

As mentioned previously, this part of the external root sheath, viz. about the 
region of attachment of the arrector muscle, contains on its surface sometimes few, 
sometimes many, smaller or larger, knoblike or cylindrical solid projections of epi- 
thelial cells. Now, in some instances, one of these grows into the depth as a 
cylindrical solid cell-mass, either making for itself a new path, i.e. becoming provided 
with a new hair-sac, or advancing in the path of the former hair ; this is the rudiment 
of the outer root sheath of the new hair. Its extremity becomes inflected over a new 
papilla, just as was the case in the foetal process. The cells of this inflected part rapidly 
increase in numbers, and thus form the bulbous extremity, in connection with which 
the hair itself and its inner root sheath are formed in exactly the same manner as in 
the embryo. Now, the new hair, as it grows upwards in the axis of the new outer root 
sheath, either passes altogether at the side of its bedhair and ultimately reaches the surface, 
its follicle becoming provided with a new neck and mouth ; or it makes its way into the 
follicle of the bedhair. In this case the hair knob being pressed by the pointed extremity of 
the new hair is gradually pushed upwards towards the free surface and finally is altogether 
ejected. Hair-follicles with two hairs, one an old hair-knob and the other a young newly 
formed papillary hair and growing from the depth, are to be explained in this manner. 

Stieda exhaustively proved the degeneration of the old papilla and the formation 
of a new one; Feiertag, Schulin, and especially Unna by his elaborate and careful 
researches, fully established it. 

Biesiadecki, v. Ebner and Remy, however, still adhere to the older doctrine 
(Langer), according to which the old papilla persists, and in connection with it the new 
hair is produced. 

The Nails. 

The nails are, like the hairs, peculiar transformations of the stratum Malpighii. 

The body of the nail, except at the free margin, is fixed over the nail-bed, while its 
root is firmly held over the nail~?natrix ) that is, the posterior part of the nail-bed, and 
is inserted in a fold, the nail groove; this being at the same time the fold by which the 
posterior margin of the nail-matrix passes into the free skin. But throughout its whole 
extent, except at the free margin, the nail is in immediate and close contact with the 
nailbed. This latter is corium covered with the stratum Malpighii. 

In a vertical section the substance of the nail appears composed of a great many 



328 ATLAS OF HISTOLOGY. 

strata of horny homogeneous transparent scales, the nail cells, which when treated with 
certain reagents show each a staff-shaped, or a discoid, much flattened remnant of a 
nucleus. The number of these strata increases from behind forwards and from the 
lateral margin towards the middle line. 

The stratum Malpighii of the nail-bed possesses exactly the same structure as that 
of other parts, with the difference that the stratum granulosum is absent in the region of 
the matrix, but is present, although only rudimentary, in the rest of the nail-bed (Hebra). 
At the nail groove the stratum corneum and stratum lucidum of the free skin pass 
a short distance over the nail-root. A similar relation exists also between the lower 
surface of the nail-margin and the adjacent skin. 

The corium of the whole nail-bed is very vascular ; its deeper portion is firmly 
connected with the subjacent periosteum by stiff bands of connective tissue. 
Together with the stratum Malpighii it is placed into permanent and regular 
folds, which are leaflike in the posterior part, including the region of the lunula, but 
low ridges in the rest of the nail-bed. The nail possesses on its lower surface 
the corresponding linear indentations, deep in the posterior portion, shallow in the 
rest. On the above folds of the nail-bed longer or shorter papillae may be met with. 

Papillae are absent in the corium of the lower part of the nail groove, and there are 
no Hands here or in the nail-bed. 

The rudiment of the nail appears in the human foetus in the third month, the 
nail groove being the first part differentiated. 

The stratum Malpighii of the foetal nail-bed in its whole extent is covered with a 
stratum corneum as in the ordinary skin, and the nail is developed and continues to in- 
crease in thickness underneath it (stratum corneum) by a conversion of the superficial 
layers of the stratum Malpighii into horny scales. This conversion extends over the 
whole surface of the nail-bed (Kolliker). 

By the end of the fifth month the front margin of the nail breaks through the 
stratum corneum, and by the seventh month the greater part of the nail has become clear 
of it. After birth the nail grows chiefly at its root by the continued conversion of the 
superficial layer of cells of the stratum Malpighii of the matrix into the nail-cells. 

Unna does not admit the correctness of the doctrine put forward by Kolliker, viz. 
that after birth the stratum Malpighii of the nail-bed outside the matrix continues to 
participate in the formation of the nail-cells, but maintains that such is the case only in 
the region of the lunula. In this he is supported by Hebra ; but, according to this 
doctrine, it is difficult to explain how the nail should be thicker in front of the lunula 
than in the region of the latter, if not by a conversion of the cells of the stratum 
Malpighii of that (viz. front) part of the nailbed. 



BLOOD-VESSELS OF THE SKIN. 320 

The Blood-vessels. 

Passing from the depth of the skin towards the surface, we find the blood-vessels 
arranged in the following systems (Tomsa) : 

a) The vascular system of the adipose tissue ; each lobule is supplied with an 
artenole which, near its entrance into the lobule, passes into the dense network of capil- 
laries ; the meshes of this have a diameter of one, two or three fat-cells ; generally two 
venous vessels originate in the periphery of the lobule ; both artery and veins join 
their respective trunks in the interlobular connective-tissue septa. The capillaries, 
of neighbounng lobules often anastomose with one another. 

6) The vascular system of the sweat glands. The arterioles ascend from the depth 
and pass ,nto a dense network of capillaries twining round the coils of the gland ■ 
special veins originate from them. The duct, however, is supplied with an arteriole 
from the superficial arteries of the corium ; the capillaries of the duct form a 
network with elongated meshes, and are connected with the capillaries of the surface 
of the corium, as well as with those of the coiled tube. 

c) The vascular system of the hair-follicles. There is a minute arteriole ascend- 
ing into the papilla, and having formed a simple or compound loop of capillaries, it 
returns as a minute vein. The capillaries of the hair-sac run between the outer longi- 
tudinal and inner circular coat, and form a network with elongated meshes. Their 
afferent arteriole comes off from the large branches in the same level as those supplying 
the papillae of the corium. 

d) The same is also the case with the arteriole of the sebaceous follicle and the 
arrector pili ; the capillaries form a dense network surrounding the alveoli of the 
former, while in the latter the meshes of the capillary network are much elongated. 
The capillaries of the hair-sac, the sebaceous follicle, and the arrector pili are continuous 
with the capillary network of the papillary body, and the efferent veins of this latter 
are at the same time the efferent veins of the former. 

e) Those arterial branches that ascend up to the surface give off, besides the 
arterioles for the sweat-duct, hair-sac, sebaceous gland, and arrector pili, as mentioned 
above, also the arterioles of the papillae. Most of the papilla: receive a minute 
branchlet, which passes into a single or compound loop of relatively wide capillaries. 
The descending branch of this passes into a network of relatively large venous vessels, 
extending horizontally in the superficial layer of the corium. The efferent veins of this 
superficial network are narrow ; they pass in an oblique direction towards the depth, 
and on their way join the efferent veins of other deeper systems. 

The corium of the nail-matrix contains a plexus of vessels with broad meshes ; in 



ATLAS OF HISTOLOGY. 
33° 
thc rest of the nail-bed it is much denser, and from it arise the vascular loops for the 

folds and ridges of the nail-bed mentioned above. 

I„ the skin of the ear-lobes, nostrils, and lips, instead of the above superhc.al network 
of venous vessels there occur venous sinuses (Tomsa), into which on the one hand open 
the capillary blood-vessels coming from the papillae, and from which on the other hand 

come off the efferent veins. 

The direct communication of arteries with veins in the skin of various localities in 
man and mammals, e.g. in the tip of the nose, finger, ear-lobe, &c, as observed by Hoyer, 
has been mentioned in Chapter XIX. p. H3- 

The Lymphatic System. 

The following description is a summary of the results of a special research on the 
Lymphatic System of the skin and mucous membranes, which I undertook for the 
Medical Officer of the Local Government Board, in whose forthcoming Reports a full 
account of it with illustrations will be given. In that account I have referred in detail 
to the observations of Sappey, Teichmann, Neumann, and others. 

The lymphatic vessels of the skin are very numerous. They may be divided into 

the following systems : 

a) The lymphatics of the connective-tissue matrix. All layers of the corium and 
subcutaneous tissue contain plexuses of lymphatic vessels, whose wall is a single layer 
of elongated spindle-shaped or sinuous flattened endothelial plates ; these vessels vary 
in breadth from place to place, and many of them are possessed of valves and corre- 
sponding constrictions. The vessels of the superficial layer of the corium are on 
the whole larger than those of the next layers of the corium, and those of the deep 
sub-cutaneous tissue are largest. As regards the direction of the plexuses, most 
of them are more or less horizontal, that is, parallel to the surface of the skin ; 
but there are vessels passing in an oblique manner through several layers of the 

corium. 

The plexuses in the different layers are denser in the corium than in the deep sub- 
cutaneous tissues. 

From the plexus of the superficial layer of the corium ascend saccular or tubular 
vessels into the papillae ; they either terminate here with a caecal extremity before they 
have reached the middle of the height of the papilla, or they form a single or even 
a compound loop. This is especially the case where the papillae are large and well 
developed, as in the skin of the finger and the scalp of man. 

In all layers of the corium, including the papillae, we find fine vessels which are 
connected on the one hand with the plexus of the corresponding layer and on the 



THE LYMPHATIC VESSELS OF THE SKIN. 331 

other terminate freely either with a pointed extremity, running out into a longer or 
shorter fine canal, or with a csecal extremity, as is the case in some papillae. These 
vessels have no valves and correspond to true lymph capillaries. 

Both the arterial and venous branches passing through the corium are either 
accompanied on one or both sides by a lymphatic vessel, or they are crossed obliquely 
by such a vessel, and then this latter appears to pass through the sheath of the blood- 
vessel. 

The lamellated connective-tissue septa between the lobules of fat-cells contains a 
plexus of lymphatics especially dense in the skin of man ; the vessels are finer and 
more numerous than immediately above or below. 

What is the relation of the lymphatics to the interfascicular spaces, and to the 
stratum Malpighii of the epidermis ? 

As has been described minutely in Chapter XXII., of the connective tissues in 
general, the lymphatic capillaries stand in an open communication, by true stomata, 
with the interfascicular spaces, which are the lymph rootlets. 

This direct mode of connection is especially marked in those lymph vessels which 
terminate or run out freely in the tissue. Another or indirect mode is this : the inter- 
stitial semifluid cement-substance of the endothelial wall of the lymphatic vessel is con- 
tinuous with the same substance of the interfascicular spaces, and formed as well as fluid 
matter may find its way from the latter into the cavity of the former. 

In the same way the lymphatic rootlets or interfascicular spaces of the papillae and 
the superficial parts of the corium, are connected intimately on the one hand with 
the interstitial substance of the stratum Malpighii, and on the other with the lymphatic 
vessels. This relation has been minutely considered in Chapter XXII. p. 175, and 
has been also referred to in this chapter, in the description of the relation of the 
stratum Malpighii to the papillary layer of the corium. 

b) The adipose tissue is supplied with a great many lymphatics ; these are: first the 
numerous lymphatic vessels which form plexuses in the interlobular connective-tissue 
septa, and secondly the intralobular lymphatics. The interlobular lymphatics are very 
much more numerous in the human skin than in that of animals. They take up every- 
where fine clefts and sinuses which are traceable between each two fat-cells. These 
represent the intralobular or intercellular lymphatics. Each fat-cell appears over a 
greater or smaller part of its circumference surrounded by a lymph-sinus. 

c) Between the coils of the sweat gland-tubes are lymph-clefts. They are bor- 
dered by the coiled tube on the one hand, and the intertubular connective tissue on the 
other, or they are contained within the latter. They are taken up by the lymphatic 
vessels of the surrounding connective tissue. Also along the duct lymph-clefts may be 

3C 



ATLAS OF HISTOLOGY. 

traced for longer or shorter distances, and the duct appears in places in half or more of 
its circumference invaginated in these lymphatics. 

d) The hair-sac contains lymph channels, which are in communication with the 
surrounding lymphatics. They form sinuses round the outer root-sheath, and pene- 
trate into the interstitial cement-substance between its (viz. the outer root-sheath's) 
epithelial cells ; this is a relation similar to that mentioned above in connection 
with the stratum Malpighii. A further connection exists between the interstitial sub- 
stance of the outer root-sheath and a space separating this latter from the inner root- 
sheath, and a similar one between this latter and the hair itself. 

e) The alveoli of the sebaceous glands are surrounded for a larger or smaller part of 
their circumference by lymphatic spaces and sinuses, connected both with lymphatic 
vessels and with the interfascicular lymph-spaces of the surrounding connective tissue. 

Elongated lymph-clefts are also found between the parts of the bundles of the 
arrector pili, similar to those observed in other unstriped muscular tissue. 

The collecting lymphatics of large or small cutaneous districts possess besides the 
lining endothelium an elastic intima, a circular muscular media, and a thin adventitia. In 
this latter are situated blood-vessels forming for the lymphatic a special system, com- 
posed of an artery, vein, and a network of capillaries (Biesiadecki). Dogiel quite recently 
demonstrated a similar network of blood capillaries on the large lymphatics underneath 
the skin of the ear-lobe and the hind extremity of the rat, and in the mesentery of the cat 
and dog. 

The Nerves. 

The nerve branches of the subcutaneous tissue contain chiefly non-medullated 
and only a few medullated nerve fibres. But the number of medullated nerves is 
greater in those localities where there are tactile corpuscles (hand, foot, glans penis). 

In the superficial part of the corium they break up into a dense plexus — which 
may appropriately be called the stroma plexus — of fine non-medullated nerve fibres, 
extending horizontally, and in close neighbourhood of the superficial network of the 
blood-vessels ; each of the nerve fibres is still possessed of its hyaline sheath of Schwann 
lined with nerve corpuscles. 

These fibres give off immediately underneath the stratum Malpighii minute varicose 
elementary fibrils, forming a network, the subepithelial network. From it fibrils ascend 
into the stratum Malpighii (Langerhans, Padkopaeff, Eberth, Eimer, Mojsisovics, 
Palladino, and others) both above the summit of the papillae and into the interpapillary 
processes ; here they ascend vertically towards the stratum lucidum. Their course 
is more or less wavy but they remain always between the epithelial cells, and when 



DISTRIBUTION OF NERVES IN THE SKIN. 333 

arrived close to the strata, bcidum are said to terminate with a minute swelling 
eit er withou piously branching or after doing so , and after running f or a sl Z 
distance m a horizontal direction : according to Eberth, in the skin in gene;,, Eimer a" 
Mojsisov.cs forthe snout of the mole, Palladino for the lips of the hoL The branched 
corpuscles ,n the stratum Malpighii, stated b y Langerhans to be terminal organs of t 
nerve fibres, have not this character (Eberth, Eimer, Palladino), but, as we mentioned 
on former occasions, belong to the lymph-canalicular system of the stratum Malpighii 

In some locaht.es (such as the hand, foot, penis, & c), medu.lated nerve fibre^ome 
off from the nerve branches of the subcutaneous tissue, and terminate each in a Pacinian 

^y r as the coded tube of the sweat glands, or deeper among the adipose tissue. 

eh:*: 'xvni : ::r ^ r - - — - - — - *- - 

Besides these endings, medullated nerve fibres may also be traced into the papilla, 
containing a tactile or Meissners corpuscle, as in the shin of the hand, foot and 
glans perns, and the lips of the mouth of man and the anthropoid apes. 

They are situated in papillae with or without capillary blood-vessels, more often in 
those that are nearer to the sweat gland duct than in those farther away (Stewart) 
1 hey are single, or occasionally but rarely double (Thin). 

Each tactile corpuscle is an oblong, oval, or curved body, enclosed in a dense con- 
nect,ve-tissue capsule, and including according to its si 2 e a larger or smaller number 
of nucleated transparent cells flattened against one another and placed transversely to 
the long diameter of the corpuscle. A medullated nerve fibre enclosed in a thick 
perineural or Henle's sheath (see Chapter XVIII.) approaches the corpuscle, the sheath 
of the former passes into that of the later, while the medullated nerve fibre enters the 
corpuscle, and, ascending towards its apex, entwines it twice to thrice. Its mode of 
termination is not definitely ascertained. 

Langerhans describes special minute budlike structures situated amongst the above 
nucleated cells which he considers as the termination of the nerve fibre. But according 
to Merkel, the tactile corpuscle is merely an aggregation of ' touch-cells ' (see p 130) • 
he describes also in other parts of the human skin, especially in that of the snout of the 
P>g, and in the small tactile hairs of the snout of the pig (Died), single and compound 
Merkel's end bulbs. (See pp. 130, 131.) 

The hair follicle is supplied with fine nerves, which have been specially investigated 
by Schobel, Burkart, Palladino, and especially Jobert and Bonnet. According to 
Jobert fine medullated nerve fibres, having run in a circular direction in the outer 
coat of the hair-sac, change into a longitudinal direction and become at the same time 



3 c 2 



ATLAS OF HISTOLOGY, 

334 



non 



non. m edu,.ated. As such they either terminate here or penetrate to the glassy men. 
bra ne along which they may be followed for some distance ; ultimately*, is perforated 
„d the nerve fibres penetrate to the cells of the outer root-sheath. The ha.r-foll.ce_ of 
the tactile hairs possesses a greater supply of nerve fibres than that of the ordinary hairs. 
According to Bonnet, all hairs, both those with an erectile body, viz. the tactile 
hairs proper, as well as those without one, viz. the ordinary hairs, possess speaal nerve- 
endings In the ordinary hairs these consist of medullated nerve fibres which in the 
region of the sebaceous gland form circular tours in the hair-sac, close to the glassy 
membrane. They pass into fine non-medullated fibres, whose real termination could 

not be ascertained. 

In the tactile hairs the medullated nerves entering the hair-sac are very numerous, 
and form superficial and deep plexuses in the outer and inner coat respectively of the 
hair-sac. They perforate the glassy membrane, terminate in peculiar end-bulbs on the 
inner surface of this latter and also between the columnar cells of the outer root- 

sheath. 

In the rat and mouse there exists a special plexus of medullated nerve fibres 
around the neck of the follicle of the tactile hairs, the nerve-ring of Schobel. 

According to Arnstein, several medullated nerve fibres ascend along the hair-sac, 
and when arrived at the neck of the hair-follicle of the skin of the back and of the ear 
of the mouse, pass into non-medullated fibres which branch into several minute fibrils, 
perforating at the same time the hair-sac ; these fibrils either terminate freely on the 
glassy membrane or they penetrate between the cells of the external root-sheath, where 
they terminate as an intra-epithelial network. A similar terminal network of fine fibrils, 
the intra-acinous network, is described by Arnstein, between the epithelial cells of 
the alveoli of the sebaceous gland. 



335 



CHAPTER XXXIV. 

THE EYELIDS, THE CONJUNCTIVA, AND THE 
LACHRYMAL GLANDS. 

The skin of the eyelids does not differ In structure in any material respect from that 
of other delicate parts of the general integument. The corium is very thin, the papillae 
very small, and the subcutaneous tissue exceedingly loose and containing very numerous 
and wide lymphatics. 

A few groups of fat-cells extend from the attached margin into the corium of 
the lid. 

The very fine hairs do not reach very deep, and they are possessed of small 
sebaceous glands ; the sweat glands are also relatively small, but do not differ from those 
of other parts of the skin. 

Large cells with pigment granules are to be met with m the connective tissue 
(Waldeyer). 

At the anterior edge of the free margin of the lid, the epidermis possesses the 
same character as on the outer skin, but the papillae become longer and the hairs are 
represented by the thick and long cilia which in all respects, including their sebaceous 
glands, resemble the well-formed thick hairs of other parts. 

They are remarkable chiefly for their rapid change and new formation (Donders). 

Immediately behind the cilia we meet with the ducts of the glands of Moll, which 
often, but not by any means always, open into the ducts of the sebaceous glands. 
Each of the former penetrates in a wavy or vertical direction into the depth of the lid 
and passes into the slightly coiled tube of the gland proper. 

The structure of the duct and gland tube is precisely the same as that of a large 
sweat gland. Also the distinction between the proximal and distal portion of the gland 
tube pointed out in the previous chapter is to be noticed here. A longitudinal layer of 
unstriped muscle cells is also here interposed between the membrana propria and the 
layer of transparent columnar epithelial cells lining the lumen of the tube (Sattler). 
The difference between this gland and an ordinary sweat gland is merely this, that the 
tube of the former is not so much coiled and that it reaches to a greater depth than the 
latter. 



6 ATLAS OF HISTOLOGY, 

Approaching the posterior edge of the free margin, but before reaching it, we meet 
with the mouths of the Meibomian glands. These are closely placed side by sule in a 
single row, and each of them possesses a straight duct which is embedded in the tarsal 
plate in the direction of the short diameter of this latter and parallel with the con- 
junctival surface of the lid. It takes up on all sides of its circumference shorter or 
longer saccular, flask-shaped, or pear-shaped single or branched alveoli. 

b But the whole gland does not extend into the distal portion of the tarsal plate (see 

below). 

As regards structure the duct and alveoli completely resemble a sebaceous gland, 

as described in the preceding chapter. The stratified epithelium of the duct is identical 
with the stratum Malpighii of the surface, i.e. the lid margin ; the marginal layer of 
small polyhedral cells, each with a spherical or slightly flattened nucleus, the central large 
polyhedral cells filled with fat globules and each containing a spherical nucleus, the 
remnants of these cells in the narrow neck of the alveoli opening into the duct, all these 
relations are the same in the alveoli of the Meibomian gland and in those of an 
ordinary sebaceous gland. When prepared with spirit and oil of cloves the intracellular 
honeycombed reticulum of the gland cells of the alveoli, whose meshes contain the above 
fat globules, is brought out in both cases with great distinctness. 

According to most observers the alveoli possess a membrana propria, but Waldeyer 
questions this ; Colosanti describes also unstriped muscle cells forming as it were a 
capsule round the alveoli. 

As the posterior edge of the lid margin is reached the stratum Malpighii becomes 
thickened and also the papillae undergo a corresponding lengthening. Passing this 
edge we arrive at the conjunctiva palpebral, a delicate vascular mucous membrane 
covered with a thin stratified epithelium, which, although modified in its constitution, is 
nevertheless a continuation of the stratum Malpighii. In most places we find it con- 
sisting of one or two layers of small polyhedral cells, on the top of which is a layer 
of longer or shorter columnar or conical cells (Klein, Waldeyer, Reich). Some of 
them are often found as mucous-secreting goblet cells (Stieda, Waldeyer). 

On the distal portion of the conjunctiva palpebral, i.e. next the fornix conjunctivae, 
the mucous membrane with its covering epithelium is placed into regular folds anastomos- 
ing with one another, hence in a vertical section through this part there appear small 
depressions of the surface which look like glandular inflections (Henle), but in reality 
are merely the furrows between those folds (Stieda, Waldeyer). The epithelium 
covering these folds diners from that covering the proximal part of the conjunctiva 
palpebral, i.e. the one next the lid margin, inasmuch as in the former its superficial layer 
is composed of beautiful columnar cells (Waldeyer). 



GLANDS OF THE CONJUNCTIVA. m 

In this region of the conjunctiva palpebrae we meet with the ducts of minute 
mucous glands, sunk into, and embedded in the tarsal plate, that is in its distal portion into 
wh.ch the Meibomian glands do not penetrate, as mentioned above. Each duct 
divides into two or three small branches and then passes into branched and convoluted 
tubdar structures, of exactly the same nature and appearance as the alveoli of mucous 
glands described on former occasions. The chief and secondary ducts are lined with a 
single layer of columnar epithelial cells, while the alveoli possess a layer of thin 
columnar mucous cells. 

These glands form the first section of the group of glands, identical in structure 
and nature, of which the greater number is situated in the beginning of the conjunctiva 
formes, ,e. next the tarsal plate. They were first discovered by Krause, and, ac- 
cording to this observer and myself and Schmidt, are much more numerous in the upper 
than in the lower eyelid. Those of the tarsal plate have been described and figured 
by myself, and afterwards by Wolfring. 

The mucosa of the conjunctiva palpebrae is a thin connective-tissue membrane 
which in the adult human subject contains a variable amount of diffuse adenoid tissue' 
This is generally better developed in the distal than in the proximal part. 

The mucosa is firmly fixed on the tarsal plate ; this is a very dense feltwork of 
bundles of fibrous-connective tissue without any cartilage, and its anterior and posterior 
surface is mtimately connected by connective-tissue bundles both with the skin section 
of the lid, and with the conjunctiva palpebral 

At the free margin of the lid the dense tissue of the tarsal plate reaches up to the 
epithelium, while at the opposite margin it is connected with the bundles of unstriped 
muscular cells representing the muscular band of Miiller. 

The central part of the eyelids, viz. that between the subcutaneous tissue of the 
outer skin and the tarsal plate, is occupied by the bundles of the striated fibres of 
the sphincter orbicularis. They are separated by a loose connective tissue, contain- 
ing occasionally also groups of fat cells. A comparatively thick layer of muscle 
fibres is pushed in between the mouths of the Meibomian glands and the cilia, and 
this is the musculus ciliaris Riolani, of which a minute portion extends beyond the 
mouths of the Meibomian glands close to the epithelium of the posterior edge of 
the free margin of the lid. 

In the foetus the epithelium covering the margin of the lids forms, by coalescence, for both lids 
one continuous mass (Schweigger-Seidel); from this epithelium the cilia and Meibomian glands 
originate, after the same plan as in the skin generally. The branched pigment cells between the 
deep layer of the epithelium and the cells of the outer root sheath of the foetal cilia are very 
conspicuous. 



33 8 ATLAS OF HISTOLOGY. 

The conjunctiva fornicis is an exceedingly delicate connective-tissue membrane 
covered with stratified epithelium of which the superficial layer is composed of more or 
less columnar cells. 

The deep portion of the membrane is very loose and contains numerous elastic 

fibrils. 

The epithelium of the conjunctiva bulbi is, like that of the fornix, stratified, but 
towards the cornea it assumes the character of stratified pavement epithelium. 

The mucous membrane of the conjunctiva bulbi contains, in man and mammals, 
a great amount of diffuse adenoid tissue, and this can be in some instances traced close 
to the corneal margin. At the limbus the mucosa forms small papillae. 

Between its deep layer and the sclerotic, and the tendons of the eye muscles, there 
is an exchange of connective-tissue bundles. 

The caruncula lacrymalis contains in its loose deep tissue fat-cells, fine hairs, 
sebaceous glands and sweat glands similar in nature to Moll's glands of the eyelids. 
There are also unstriped muscular fibres in its tissue. The surface is very uneven and 
except at the summit, where the epithelium is like the stratum Malpighii, it is com- 
posed of a superficial layer of columnar and one or two deep layers of small polyhedral 
cells. In the caruncula lacrymalis of two negroes Giacomini found, similar to what is 
the case in the ape, a minute cartilage, which possessed the structure of fibro-cartilage. 

The distribution of the blood-vessels in the human eyelids has been specially and 
minutely investigated more recently by Fuchs and Langer. 

The distribution of the blood-vessels of the skin of the eyelids, of the cilia, and 
glands of Moll is similar to that in the skin of other localities. 

A rich superficial network of capillaries is present in the conjunctiva palpebral, 
the limbus, and the caruncula lacrymalis. 

In the conjunctiva palpebral the superficial network is very close, and so is also 
that surrounding the alveoli of the Meibomian glands. 

A rich plexus of vessels, chiefly veins, distinguishes the conjunctiva bulbi. 
The lymphatics of the conjunctiva form, according to Schmid, a superficial and deep 
network, connected with one another by many short branches. The vessels of the 
superficial network are very fine, and some of them terminate with a pointed or caecal 
extremity. The vessels of the deep plexus are possessed of valves. The superficial 
network is densest at the limbus corneae ; both in the conjunctiva bulbi and in the 
limbus the lymphatics stand in direct communication with the interfascicular lymph-clefts 
of the sclerotic and cornea respectively (Recklinghausen, Leber, Waldeyer). 

I have found the superficial network of the conjunctiva pelpebrae exceedingly 
dense, and its vessels diminishing in size towards the lid margin. 



LYMPHATICS OF THE CONJUNCTIVA. 



339 



The deep plexus lies close to the tarsal plate, a few vessels passing from the former 
through the latter join the lymphatics of the intermuscular connective tissue of the 
sphmcter orbicularis. At the free margin of the lid the lymphatics of the conjunctiva 
palpebne pass directly into those of the skin (Fuchs). 

The sinuses around the alveoli of the Meibomian glands (Czerny) are in direct 
connection with lymphatic vessels (Fuchs). 

The efficient lymphatics of all parts of the conjunctiva run towards the angles of 
the eyelids. 

_ As mentioned above, the conjunctiva in the adult human eye contains in many 
instances dtffuse adenoid tissue. According to Stieda, and especially Morano, real 
lymph folhcles occur also occasionally in the human conjunctiva, but this is denied by 
Sattler and others. 

In the case of many mammals definite groups of lymph follicles, like those of the 
tonsils, are a common occurrence about the inner eye angle (Kleinschmidt, Frey 
Huguenin, Schmid and Waldeyer). Bruch saw them first in the conjunctiva of 
the lower eyehd of cattle, and they are here known as the glands of Bruch In the 
third eyelid of the rabbit, sheep, cattle, these lymph follicles form a conspicuous 
part. 

Frey and Huguenin traced lymph sinuses and clefts, situated between the follicles 
into the lymphatic vessels of the conjunctiva. Also Waldeyer followed the lymphatic 
vessels in the lower eyelid of cattle up to the glands of Bruch. 

The Nerves.— The nerve branches are composed of medullated fibres. When 
arrived at near the surface they lose their medullary sheath, but retain their hyaline 
sheath of Schwann and the nerve corpuscles, and anastomose into a plexus, the sub- 
epithelial plexus of Arnold. From this very fine primitive fibrils are given off, which, 
having run a short distance underneath the epithelium, ascend between the cells of 
this latter, where most of them terminate in a network (Helfreich, Morano). 

Krause showed the existence of small tactile corpuscles in some of the papilla? near 
the ciliae ; as in other places, they are also here connected with a medullated nerve 
fibre. 

The termination in end-bulbs of Krause in the conjunctiva of man and calf has been 
mentioned in Chapter XVIII. p. I2g . In the conjunctiva palpebral medullated nerve 
fibres accompanying the blood-vessels are described by Colosanti ; they lose their 
medullary sheath while perforating the membrana propria of the alveoli of the Mei- 
bomian glands, and terminate as a network of fine non-medullated nerve fibres between 
the gland cells. 



3D 



34 o ATLAS OF HISTOLOGY. 

The Lachrymal Glands. 

These correspond in structure to the true salivary glands. A connective-tissue 
capsule is in connection with the septa by which the gland is divided into lobes and 
lobules. 

The larger or interlobular ducts are lined with a layer of thin columnar cells ; the 
intralobular branches, the lachrymal tubes of Boll, are lined with a layer of columnar 
cells, whose external portion, just like those of the corresponding parts in the salivary 
glands, appears very distinctly fibrillated ; the inner portion, that is the one next the 
lumen, is only slightly striated. The nucleus is situated in about the middle of the 
cell. 

Each branch of the intralobular ducts passes through an intermediate portion into 
the alveoli. The former is a long fine tube lined with a layer of flattened cell-plates, 
often imbricated with their margin (Boll). These cells are traceable into the interior 
of the alveoli as the centroacinar cells, similar to what has been observed by Langerhans 
in the pancreas. The alveoli are longer or shorter, tubular, more or less convoluted 
structures, possessed of lateral and terminal tubular or saccular branches. 

The membrana propria is composed of homogeneous flat branched cells, from 
which membranous septa penetrate between the epithelial cells of the alveolus. These 
latter are a single layer of polyhedral, cubical, 'granular '-looking cells, each with a 
spherical nucleus, and in this respect they completely resemble the lining cells of the 
alveoli of the serous or true salivary glands. 

The central fine lumen of the alveoli and its connection with the intercellular sub- 
stance, or, what some observers call the intercellular capillary ducts, is the same as in 
other glands, and has been fully described in connection with the salivary glands ; see 
Chapter XXIV. p. 190. 

Reichel studied the state of the alveoli in rest and during secretion, and found that 
in the former condition the lining cells are well defined, conical or cylindrical, and com- 
posed of a transparent, slightly granular protoplasm, each possessed of an irregular 
nucleus situated in the outer third ; while during secretion the cells are smaller and very 
opaque and granular, and their outlines not well defined, the nucleus being at the same 
time spherical and placed centrally. 

The distribution of the blood-vessels is identical with that of the salivary glands. 
The terminal distribution of the nerves is not known. The lymphatics form a 
plexus of valved vessels in the interlobular connective tissue ; they take up large lymph 
sinuses surrounding the alveoli, which form a continuous system of spaces (Boll). 

Harder s gland, occurring in most mammals on the inner angle of the eye, and 



STRUCTURE OF HARDERS GLANDS. 34 1 

closely placed against the surface of the eyeball and the inner margin of the nictitating 
membrane, has been carefully studied by Wendt. It bears a definite relation to the 
lachrymal glands, being larger in those animals which possess only small lachrymal 
glands and vice versa. Wendt finds that in the rodents, as mouse, rat, and guinea pig, it 
resembles a large compound sebaceous gland ; in the ox, sheep, and pig it is, however 
ident.cal with the lachrymal gland, i.e. is a serous gland, while in the rabbit and hare it 
cons. S ts of two different sections, of which the upper smaller one appears white and 
resembles the sebaceous gland, while the other, viz. the lower one, is larger, and in the 
fresh state rose-coloured ; its structure is the same as that of the lachrymal glands ; its 
alveoli are lined with pyramidal cells, whose protoplasm shows a reticular nature 
Injecting the alveolar cavities from the ducts, it is seen that the injection-matter 
penetrates into the interstitial cement-substance between the epithelial cells. Wendt does 
not admit that the membrana propria of the alveoli of the rose-coloured or serous portion 
of the adult gland is a basket-shaped network of ilat branched nucleated cells as 
described by Boll and many others (see former chapters), but considers it a homogeneous 
non-nucleated membrane. 

Giacomini found a rudiment of the Harder's gland also in the Cercopithecus, 
Cynocephalus, and man.' 



3D: 



342 



ATLAS OF HISTOLOGY. 



CHAPTER XXXV. 

THE CORNEA AND SCLEROTIC. 

The cornea consists of the anterior epithelium, the anterior elastic or Bowman's 
membrane, the substantia propria, the posterior elastic membrane or membrana 
Descemeti, and the endothelium lining the posterior surface. 

i) The anterior epithelium is a stratified pavement epithelium of a similar nature 
as that of other regions : viz. the deepest layer is composed of columnar cells, each with 
an oval nucleus ; then follow two or three layers of polyhedral cells, each with a spherical 
nucleus, they and their nucleus become flattened towards the surface ; finally there are 
two or three superficial layers of scales, each with a discoid nucleus, more or less oval in 
outline. 

The cells of the deepest layer are of different heights, club-shaped, cylindrical, 

pear-shaped ; the deep extremity by which they are fixed on the subjacent tissue is 
flattened and plate-like, the foot-plate of Lott and Rollett. But neither in this, nor in 
the fact that many of the polyhedral cells of the middle layers possess instead of smooth 
surfaces one, two, or three pitlike depressions to receive the convex surfaces of their 
neighbours (Kolliker, Cleland), does the epithelium of the cornea differ from other 
stratified epithelium. The cells both of the deepest and middle layers are in most 
instances prickle cells. 

The nucleus of the deepest cells contains a delicate regular reticulum, without any 
nucleoli, that of the cells of the middle layers a less uniform reticulum and often one or 
more thickenings in it, nucleoli. 

The very same changes of the intranuclear network that we described in Chapter 
XXXIII. leading to the division of some of the nuclei of the deepest cells are also here 
to be noticed, and have been observed in the normal and inflamed state by Mayzel and 
Eberth. They will be referred to in detail in a future chapter. 

The division of the cells takes place chiefly in the deepest layer (Lott), and as in 
other places the next following layer of polyhedral cells owes to this its origin. 

But that in this process of division some of the deepest cells divide into a nucleated 
polyhedral top-cell and a deep mass of protoplasm which at first is without any nucleus 
but in which afterwards a nucleus is formed de novo, as maintained by Lott, Krause and 
others, is most decidedly erroneous, and I fully agree with Flemming on this point, viz. 



EPITHELIUM OF THE CORNEA. 343 

that the division of the cell is always subsequent to the division of the nucleus, and that 
this invariably takes place after the indirect manner described on former occasions. 
There is at no time a cell to be found in the deeper or other layers that does not possess 
a nucleus. 

Amongst the epithelial cells of the middle strata are seen branched spaces 
in the interstitial cement-substance ; the processes of these spaces lose themselves 
in the cement-substance. The spaces contain branched nucleated corpuscles which on 
the warm stage show distinct though slight amoeboid movement. They have been 
noticed in the epithelium of the cornea of the frog and mammals (Ribbert, Raehlmann), 
and correspond to the similar spaces and cells described on former occasions as present 
in every epithelium and as representing the intraepithelial rootlets of the lymphatic 
system. 

The lower surface of the epithelium is in most instances smooth and firmly fixed 
on the anterior elastic membrane, but occasionally, especially in the human cornea 
prepared with spirit, appears as if possessed of very minute teethlike spikes let into 
minute depressions of the elastica anterior (Henle, Langerhans). 

The epithelium of the cornea is directly continuous with that of the conjunctiva, 
but differs from it in many respects; the former is conspicuously more transparent, 
and its layers more numerous. In dark eyes of animals (sheep, dog) the epithelium 
of the conjunctiva contains pigment, and this ceases suddenly at the margin of the 
cornea, not being continuous into the epithelium of this latter. 

2) The elastica anterior or Bowman's membrane is a transparent homogeneous- 
looking membrane, distinct from the subjacent substantia propria and continuous with 
the basement membrane of the conjunctiva. It contains indications of bundles of minute 
fibrils, and is not continuous by bands of connective-tissue fibrils with the substantia pro- 
pria, nor does it contain cellular elements (corneal corpuscles) as maintained by Waldeyer. 
The elastica anterior is best developed in the human cornea, less so in that of most 
mammals. In rabbit it is also distinct, but not in dog, in the latter case it is reduced to 
a very delicate layer. 

Bowman's membrane is perforated by a few thin channels passing through it in an 
oblique manner (Engelmann), they are channels containing nerve branches, the rami 
perforantes (see below). 

3) The substantia propria is composed of lamellae of bundles of fibrillar connective 
tissue. The bundles amongst themselves and the fibrils within a bundle are united 
by the usual semi-fluid albuminous interstitial cement-substance, which is easily 
dissolved by a ten per cent, solution of common salt (Schweigger-Seidel). The bundles 
of these lamellae run in a direction parallel to the surface of the cornea, but not 



344 ATLAS OF HISTOLOGY. 

only groups of bundles of adjacent lamellae, but also those belonging to the same 
lamella, cross under right angles. Neighbouring lamellae anastomose with one another, 
owino- to bundles passing between them ; but in this respect there exist great differences 
in the different sections of the cornea, in the anterior section such bundles are much more 
numerous than in the posterior. Near the elastica anterior some of these bundles pass 
through several lamellae in an oblique manner and represent the fibrae arcuatae. 

There are few isolated delicate elastic fibrils to be met with between the lamellae 
(Henle), they are only seen from place to place. 

The interstitial cement-substance is collected as a distinct layer between each 
two adjacent lamellae. In each layer of this interlamellar substance lies one layer of 
lacunae and their anastomosing canaliculi, first discovered by v. Recklinghausen and 
named by him the lymph-canalicular system. They do not possess any limiting mem- 
brane, although such an one has been ascribed to them by Leber, Lavdowsky, and 
others. 

Their arrangement, shape, and differences in different animals have been fully 
considered in Chapters IV. and XXII. In most instances the lacunae are flat, more or 
less oblong, and possessed of numerous canals of various thicknesses, most of them 
being branched and anastomosing with those of neighbouring lacunae. In the cat they 
are in groups (Strieker), so that two or three or more lacunae are in contact with one 
another and joined into larger cavities. 

A similar grouping of lacunae is generally found in the anterior sections of the 
young cornea. 

The lacunae of the anterior sections are generally larger and less branched than 
in the deeper parts of the cornea (His). 

Each lacuna contains the nucleated plate of a cell, the corneal corpuscle. Each of 
these is possessed of processes extending into the above canaliculi, and by them the 
corneal corpuscles anastomose in a network. The lacunae and canaliculi are not 
completely filled out with the branched corneal corpuscles, and there is enough room 
left for the circulation of plasma irrigating the tissue, and for the passage of migratory 
cells, and in many places also for the nerve fibrils (Recklinghausen, Strieker, Rollett, 
and others). 

Most lacunae and the corpuscles are flat in a direction parallel to the surface of the 
cornea, but in every preparation there are some found whose narrow side is looking 
towards the surface of the cornea. The lacunae or corneal corpuscles respectively of 
neighbouring layers anastomose with one another (Rollett). 

Each corneal corpuscle consists of a hyaline ground-plate, in which is embedded an 
oval nucleus. Around this nucleus is a ' granular '-looking protoplasm, which is in reality 



CORNEAL CORPUSCLES. 345 

a very dense reticulum of fibrils ; this substance is continued into the processes (see 
Chapter IV.). As has been stated on p. 29, this distinction into a ground-plate and 
a ' granular'-branched part of the corneal corpuscle probably accounts for the opposing 
views of the nature of the corneal corpuscles : Hoyer and Schweigger-Seidel consider- 
ing them merely as endotheloid plates without processes, these latter being artificial 
products ; Strieker, Rollett, Waldeyer, and others, as more or less branched cells, while 
still others, Thanhoffer, Thin, Henle, assume altogether two types: one, the endotheloid 
cells and the other, the branched typical corneal corpuscles. The nucleus in most 
instances is limited by a distinct membrane and includes a delicate intranuclear 
reticulum, which under certain reagents shows one or two larger collections, nucleoli. 
But in the fresh state and under suitable circumstances it can be ascertained that the 
reticulum is uniform and is connected with the intracellular fibrils. We meet with 
many corneal corpuscles, whose nucleus does not possess any definite membrane, and 
whose intranuclear network is therefore not separated from the intracellular one, but 
owing to the much greater density of this latter (intracellular network) is nevertheless 
well marked off from it. 

The corneal corpuscles are endowed with slight contractility, observed in the 
normal state, under the influence of thermal, electrical and mechanical influences (v. Reck- 
linghausen, Kuhne, Mayzel, Rollett, Waldeyer), and under inflammatory conditions 
(Strieker and Norris, Rollett and others). 

In the normal state very few migratory cells can be detected in the lacunar system 
of the cornea, but under inflammatory conditions their number greatly increases (pus 
corpuscles), and they may be seen squeezing themselves through even the finest 
canaliculi. Owing to their moving in the lymph-canalicular system they then present 
themselves chiefly in elongated shapes. 

4) The elastica posterior or the membrana Denemeti is a very strongly resistent 
elastic membrane. It is present in the cornea of all mammals as a very conspicuous 
structure. Although of a hyaline aspect it is nevertheless composed of bundles of very 
delicate fibrils (Tamamscheff, Schweigger-Seidel). 

5) The posterior surface is covered with a single layer of polyhedral slightly 
flattened granular-looking endothelial cells, each with a single oval slightly flattened 
clear nucleus containing under some conditions a single or double nucleolus. Klebs, 
Strieker, and Norris attribute to these cells amoeboid movement. 

According to v. Ewetsky, each endothelial cell is composed of a superficial hyaline 
plate and a subjacent protoplasmic nucleated portion. Swaen maintains that the 
endothelium of the frog s cornea consists of two layers : a superficial layer of proto- 
plasmic contractile, and a deep layer of hyaline non-contractile cells. 



346 ATLAS OF HISTOLOGY, 

In some instances in the fresh state and after reagents, especially after hardening, 
the cells appear separated from one another by small globular spaces. Under abnormal 
conditions these increase in number and size, and the cells appear hereby changed into 
more or less branched corpuscles, connected by their processes. 

As will be minutely described in a future chapter, Mayzel observed indirect division 
of the nuclei of these cells. 

With the exception of the very margin there are no blood-vessels in the cornea. 
The foetal cornea possesses a network of capillaries extending underneath the anterior 
epithelium over the whole surface of the cornea, as the precorneal, vascular network. 
But a short time after birth all vessels disappear, except those at the margin of the cornea, 
where they terminate in arcuate loops directed towards the centre of the cornea. These 
vessels carry a small amount of connective tissue from the conjunctiva into the cornea. 

The Lymphatics. — There are no proper lymphatic vessels in the cornea. As has 
been mentioned on a former page, the lymphatics of the conjunctiva anastomose at the 
limbus with the interlamellary lacunar system of the margin of the cornea. A similar 
communication exists between the lacunar system and the perivascular lymphatics of 
the blood-vessels in the marginal portion of the cornea (v. Thanhoffer). The lacunar 
system is an intercommunicating system for the whole cornea. Injections into the 
lacunae of the superficial layers of the cornea penetrate also into the interstitial substance 
of the deep epithelial cells of the anterior surface (Leber). All nerves from the larger 
branches to the finest fibrils of the substantia propria are contained in the interlamellar 
cement-substance, very often passing through the lacunar system and its canaliculi- 
The larger nerve branches are possessed of a perineural sheath which, just as in other 
places, is composed of a single layer of endothelial plates (v. Recklinghausen, Durante, 
Thanhoffer, Thin, see pp. 85 and 125), but this endothelial membrane cannot be said 
to represent the endothelial wall of a lymphatic vessel in the accepted sense. 

The corneal tubes of Bowman, which present themselves in the cornea into whose 
tissue injection matter had been forced, are artificial products (Rollett), being shorter 
or longer spaces dug out in the interstitial cement-substance between the bundles of 
one and the same lamella, or long canals dug out between the lamellae. 

The Nerves of the cornea have been described on p. 125, but I wish here to make 
a few additional remarks concerning their termination, having lately had the opportunity 
of a renewed inquiry into this subject. The detailed account of this will be found in the 
1 Journal of Micr. Science,' October, 1880. 

The nature and arrangement of the branches of the subepithelial plexus or stroma 



DISTRIBUTION OF FINE NERVES OF CORNEA 



347 



plexus (Waldeyer) have been described and figured on a former occasion (see Plate 

XXIV.). 

The fine nerve fibrils which form the subepithelial network are derived from the 
branches of the stroma-plexus in two different ways : either through the rami perforates 
breaking up into bundles of minute fibrils, or directly from the stroma-plexus as single 
primitive fibrils or as small bundles of them. The former is the more common mode. In 
the latter instance, viz. when derived directly from the stroma-plexus, previously to enter- 
ing the subepithelial network, they branch, and some of them running for a long distance 
within Bowman's membrane ultimately enter the subepithelial network, as mentioned 
before, while others do not enter Bowman's membrane, but remain in the super- 
ficial layers of the substantia propria, where, after branching, they terminate ; these 
are the deep fibrils of Hoyer's subbasilar plexus. Similar fine nerve fibrils are 
met with in most parts of the substantia propria, but they are most numerous in the 
anterior layers. In the frog's cornea they are exceedingly abundant and compressed, as 
it were, into a relatively thin stratum, next the membrana Descemeti. Their very 
great length, their relatively few branches, and their peculiar straight course are very re- 
markable. In some places they seem to run in a straight line, without branching, and 
after a shorter or longer course they bend sharply into a direction at a right angle. In 
other places they, as well as their branches, run a wavy course, or they change their course 
under right angles in rapid succession. As has been mentioned above, the minute nerve 
fibrils, coming off from the subepithelial network, enter the epithelium and, having 
ascended into the middle and superficial layers, give off lateral branches ; both, viz. the 
primary fibrils as well as their branchlets, pursue a longer or shorter horizontal course 
between the epithelial cells, but in a more or less wavy manner, and parallel with the sur- 
face, repeatedly changing their level. These fibrils give off a good many lateral branches, 
and anastomose with one another in but few places. What has not been observed 
before is this : whether the fibrils are next to the superficial layer of epithelial cells 
or not, they are possessed of exceedingly numerous very fine lateral branchlets, 
which in ordinary gold specimens are not marked at all, or only as minute rodlike 
prominences, sticking out at the side of the above fibrils ; in perfect specimens, how- 
ever, they are seen to be the commencement of exceedingly delicate fibrils, which branch 
dichotomously like the twigs of a tree and break up into a network of very short rods. 
This ultimate network lies between the epithelial cells and occurs in most layers, 
except the deepest and the most superficial layer. 

Many of the intraepithelial nerve fibres, especially the finer and finest ones, are 
often seen to possess smaller or larger, spherical or angular, varicosities, just like the 
fibrils of the subepithelial network (seep. 125). That the intraepithelial nerve fibrils 

3 e 



ATLAS OF HISTOLOGY. 

34 y 



seem 



„ to terminate with such a varicosity or end-knob has been asserted by Cohnhe.m, 
Tolotschinow, Lavdowsky, Krause and others ; but they are not at all constant (Hoyer, 
Klein Izquierdo), and, as I have shown just now, are not the real termination. 

The fine nerve fibrils of the substantia propria enter into close relation with the 
lacunar system or the corneal corpuscles respectively, for every one of these fibrils 
running in the interlamellar cement-substance must of necessity pass through or by a 
lacuna and its canaliculi. And the fact of this relation may be, and probably is, the cause 
of the assertions of so many observers of a direct anatomical connection of these nerve 
fibrils with the corneal corpuscles (Kuhne, Lippmann, Moseley, Lavdowsky, Thanhoffer, 
Izquierdo and others). In mammals they branch, and by these branches anastomose 
only in very few places ; in the frogs cornea such anastomoses are oftener met with. It 
is very difficult to ascertain the real termination of the fine nerve fibrils. In ordinary 
preparations they seem to run out freely in the tissue, but in isolated instances of perfect 
cold specimens of the cornea of the rabbit and the kitten, as well as of the frog, I have 
ascertained that they terminate with an exceedingly delicate network of fine and short 
fibrils, situated not in, but on the surface of the corneal corpuscles. 

The Sclerotic. 

The sclerotic membrane is of a dense texture, similar in structure to that of the dura 
mater or a fascia. It consists of groups of bundles or trabecular of fibrillar connective 
tissue crossing each other in different directions, with a slight tendency to a lamellar 
arrangement. Between the groups of bundles are the interfascicular lymph-spaces con- 
taining the flattened branched connective-tissue cells, identical in shape with those of the 
cornea. This connective-tissue matrix passes into that of the cornea, the bundles be- 
coming, however, more transparent. In most dark-eyed mammals we find near the point 
of transition the connective-tissue cells of the sclera containing brown pigment granules, 
but they are absent in the corneal tissue. 

Near the ligamentum pectinatum the bundles of the sclerotic become more regularly 
arranged, being parallel with one another in a more or less annular direction. 

Between the bundles of all parts we meet with networks of fine elastic fibrils ; these 
are especially numerous near the ligamentum pectinatum. 

On the inner surface of the sclerotic the trabecular arrange themselves in some 
places into thin lamellae, and these pass in company with blood-vessels from the inner 
surface of the sclerotic to the outer surface of the chorioidea. The portion of this 
tissue next the inner surface of the sclerotic is known as the lamina fusca, that next 
the outer surface of the chorioidea as the suprachorioidal tissue. The connective- 
tissue corpuscles of these lamellae are likewise flattened, and some are much less branched 



STRUCTURE OF SCLEROTIC MEMBRANE. 349 

than others, their processes being fewer, and shorter, and broader. (In dark eyes many 
of the cells contain yellowish or brownish pigment granules ; see below.) 

The lamella are covered with an endothelium, and are separated from one another 
by more or less continuous lymph-spaces (Schwalbe). 

As regards the outer surface of the sclerotic various regions are to be dis- 
tinguished, viz. the subconjunctival region, then that of the insertion of the tendons of the 
eye muscles, and the region of the Tenonian lymph-space. The bundles of the subcon- 
junctival loose connective tissue, and those of the tendons are intimately connected with 
those of the sclerotic. In the region of the Tenonian lymph-space (Schwalbe) the 
proper tissue of the sclerotic is covered with a thin layer of connective tissue ; this is 
the inner or episcleral lamina of the Tenonian capsule (Schwalbe) ; the inner surface of 
the outer lamina and the outer surface of the inner lamina are lined with an endothelial 
membrane (Schwalbe). 

Helfreich describes in the tissue of the sclerotic a dense plexus of non-medullated 
nerve-fibres. Waldeyer saw in the human sclerotic repeated divisions of axis cylinders. 
In the superficial layers such fine branches may be followed for a considerable distance 
accompanying the blood-vessels. 

The sclera contains its own blood-vessels, consisting of arterioles, capillary and 
venous networks. The capillaries and veins are distinguished by an outer special 
endothelial sheath (Michel). The tissue of the sclera is, besides, perforated by the vessels 
destined for the chorioidea. 

The above-named interfascicular lymph-spaces form an intercommunicating system ; 
which has been beautifully demonstrated by Michel in injections into the sclerotic. 
There exists, in the immediate neighbourhood of the ligamentum pectinatum iridis, at 
the point of junction of the cornea and sclerotic but belonging to the sclerotic, a 
circular canal, compressed in a direction parallel to the surface of the sclerotic, lined with 
a special endothelial membrane ; it forms an indirect communication with the inter- 
fascicular lymph -spaces of the surrounding parts of the sclerotic. This is the canal of 
Schlemm. 

According to Schwalbe the canal of Schlemm, like the spaces of Fontana, with 
which it communicates, is a lymph-canal, but according to the more recent investigations 
of Leber, it is a venous plexus, while Waldeyer considers it with Schwalbe as a lymph- 
space. It communicates with the anterior chamber of the eye (Schwalbe), anastomos- 
ing by fine clefts and holes with the spaces of the ligamentum pectinatum. 

This latter is a spongy tissue situated at the point of junction of the cornea and 
sclerotic on the one hand, and the iris, ciliary processes and ciliary muscle on the other. 
The trabecule and lamella? which constitute its matrix are composed of elastic fibres, 

3 E2 



,, ATLAS OF HISTOLOGY. 

thick and thin ones, arranged as a network ; this is in many instances so close that more 
or less complete elastic membranes (fenestrated membranes) are hereby formed (Henle, 

Schwalbe). 

Next the cornea and next the insertion of the ciliary muscle the fibres assume a 
special annular direction as the anterior and posterior limiting ring of Schwalbe. 

The trabecule and lamellae are embedded or ensheathed in a more or less 
hyaline elastic substance which is a direct continuation of the membrana Descemeti ; 
their free surface is covered with a layer of flattened polyhedral endothelial cells 
directly continuous on the one hand with the endothelium of the membrana Descemeti, 
and on the other with a similar layer of cells covering the anterior surface of the iris. 

The connection of the ligamentum pectinatum with the sclerotic is also a very inti- 
mate one, since the elastic fibrils between the connective tissue trabecular around the 
canal of Schlemm pass directly into those of the former. 

The continuity of the ligamentum pectinatum with the iris, processus ciliares and mus- 
culus ciliaris, is effected in this way: The elastic trabecular and lamellae of ■ the spongy 
substance of the ligamentum pectinatum pass directly into the tissue at the root of the 
iris, hereby they retain their arrangement as a spongy substance ; in some mammals 
the spaces are here very considerable and are called the spaces of Fontana. 

The membrana Descemeti, which, as we have mentioned above, is continued over the 
ligamentum pectinatum, passes directly into the delicate basement membrane of the 
anterior surface of the iris. The continuity of the endothelium has been mentioned 
above. From the matrix of the iris and processus ciliares, especially the former, tra- 
becular of connective-tissue bundles with elastic fibres pass into the matrix of the 
ligamentum pectinatum ; these trabecular, the iris-processes of Rollett, are also covered 
with a continuation of the membrana Descemeti (Konigstein, Briggs) and are very con- 
spicuous in pigmented eyes both in man and mammals, owing to the branched 
connective-tissue cells contained between their bundles being pigmented. 

The elastic tendons of the meridional portion of the ciliary muscle are continued 
into the elastic trabecular and lamellar of the ligamentum pectinatum. 



35i 



es 



CHAPTER XXXVI. 
THE IRIS, CILIARY PROCESSES, AND CHORIOIDEA. 

r. The Iris. 

sTlce: 3 COnSlStS ° f ^ fOl ' 0Wing IayerS ' C ° Unting fr ° m thC anteri - '0 the posterior 
a) The endothelium consists of polyhedral cells, each with a spherical or slightly 
oval nucleus ; ,n dark-coloured eyes of man and mammals the cell substance is filled with 
dark brown pigment granules. 

6) Underneath the endothelium is a very delicate hyaline basement membrane ■ its 
continuity with the hyaline elastic membrane of the ligamentum pectinatum and with 
Descemeti's membrane has been mentioned above. 

*) The substantia propria : this forms the matrix of the iris and consists of bundL 
of connects tissue chiefly accompanying the blood-vessels ; near the ciliary margin 
especially towards the posterior surface, they are arranged in larger groups densely inter- 
woven with one another. 

Between these bundles of connective tissue are found very numerous branched 
cells ; ,n dark eyes many of them contain a variable amount of pigment granules. Both 
the unpigmented and pigmented cells are generally elongated, slightly flattened, and with 
thin processes, which, extending chiefly in the level of their broad diameter, cause that 
the cells when viewed in profile appear more or less spindle-shaped, with only few pro- 
cesses. Around the blood-vessels and near the posterior surface these pigment-cells are 
most numerous. In the latter place they are very closely arranged, and being parallel 
to the surface form almost a layer of their own. 

Besides these branched cells there are a few migratory cells to be met with in the 
sheath of the blood-vessels. 

d) A hyaline thin layer, being a kind of basement membrane ; it is a continuation 
of the lamina vitrea of the ciliary processes and bears also the name of membrana 
pigmenti. 

e) The uvea ; this is composed of polyhedral epithelial cells each with an oval or 
spherical nucleus ; the cell substance is in all instances, albinos excepted, filled with 
dark brown pigment granules. In blue eyes this is the only layer of the iris that contains 
pigment granules. 



352 ATLAS OF HISTOLOGY. 

According to Hirschberg and Loewe the pigmented epithelium of the posterior 
surface consists of two layers : a superficial and a deep one ; the former being continuous 
with the pars ciliaris retinae, the latter with the uvea of the processus ciliares. 

Near the pupillary margin are the circular bundles of unstriped muscle fibres of the 
sphincter pupilke ; they are situated nearer to the posterior than to the anterior surface 
and diminish in breadth towards the pupillary margin. They are separated from one 
another by small masses of the iris stroma. At the pupillary margin the muscle fibres 
of the sphincter are continuous with a thin membrane of muscle cells extending over 
the whole posterior surface of the iris (Henle, Hiittenbrenner, Ivanoff), but under- 
neath the above superficial layer of pigment cells, to the ciliary margin, where its 
muscle cells change into a circular direction and anastomose into a plexus (Ivanoff). 
These muscle cells are all directed from the pupillary to the ciliary margin and 
represent the dilatator pupillae. 

The Blood-Vessels of the Iris. — The arterial vessels are those derived from the 
•circulus arteriosus major and from the ciliary processes. The superficial layer of the 
tissue of the iris contains the capillary networks ; these are densest near the posterior 
surface, and form a continuation of the capillary network of the ciliary processes ; the 
sphincter pupillae has its own dense capillary network. 

The veins follow the arterial branches and just like these are situated chiefly in 
the middle layer of the stroma. 

The adventitia and media of the arterial vessels is very thick and in the latter 
especially muscular (Arnold, Hiittenbrenner). 

According to Faber there exists a direct transition of arterial vessels into venous 
branches. 

The Lymphatics. — The iris has no lymphatic vessels in the ordinary sense, but 
there exist lymphatic sinuses in the sheath of the blood-vessels, especially of the arteries 
and between the trabecular of the connective-tissue bundles; at the ciliary margin of the 
iris they open into the spaces of Fontana and into those of the ligamentum pectinatum. 

The Nerves of the iris are very numerous and the number of the medullated 
nerves is in direct proportion to the muscular tissue. The human iris possesses fewer 
nerves than that of mammals, and this again fewer than that of birds (Pause). 

The nerves are arranged, according to Arnold, Formad, Faber, and others, in this 
manner : in the outer or ciliary portion of the iris the nerve branches form a plexus ; 
from this are derived : [a) non-medullated fibres terminating as a delicate network on 



STRUCTURE OF THE CILIARY PROCESSES. 355 

the dilatator ; (6) medullated nerves passing eventually into fine non-medullated fibrils 
arranged as a network close to the anterior surface ; and (c) a network of non-medullated 
fibres belonging to the sphincter pupilta. 

According to A. Meyer, there are in addition fine non-medullated nerve fibrils 
which accompany the capillary blood-vessels and are connected into a network. 

According to Faber there are ganglion-cells contained in the nerve networks of the 
iris. 

2. The Ciliary Processes. 

These consist of a matrix which is similar to that of the iris, being a continuation 
of it ; it is chiefly composed of bundles of connective-tissue fibres with pigmented 
branched corpuscles between them. These are most numerous in the part next to the 
chorioidea. Elastic fibres are also to be met with. The stroma is directly continuous 
with the tissue of the ligamentum pectinatum, as mentioned above. The part nearest to 
the sclerotic is of loose texture and contains the larger vascular branches; the super- 
ficial layer of the ciliary processes contains the capillary blood-vessels. 

The stroma of the ciliary processes is covered on its free surface with a glassy 
hyaline membrane, lamina vitrea, in which on being treated with certain reagents, ten 
p. c. saline solution amongst others, bundles of fine fibrils can be detected. It is a con- 
tinuation of the basement membrane on the posterior surface of the iris, but is much 
thicker and possessed of a network of folds (H. Muller), the meshes of which are much 
closer towards the iris than towards the chorioidea. 

The pigmented epithelium or uvea, which follows behind the lamina vitrea, is a 
continuation of the same layer of the iris, and is identical with it in structure. 

Finally, the uvea is covered with the pars ciliaris retinae, a single layer of columnar 
transparent cells, each with an oval nucleus (see below). 

The space between the ligamentum pectinatum, sclerotic, ciliary processes and 
adjoining portion of the chorioidea is occupied by the ciliary muscle, originating at the 
ligamentum pectinatum. Nearest to the iris are the few circular bundles of the portio 
Mullen, while the radiating part occupies the root of the ciliary processes, in fact causes 
the projection of them ; the greater portion of the muscle, however, has a meridional 
direction, and extends from the ligamentum pectinatum between the sclerotic and ciliary 
processes and chorioidea, for a considerable distance backwards. It is separated from 
the sclerotic by the thin lamina fusca. 

The bundles of this muscle are arranged in lamellae, separated from one another by 
connective tissue, of which in dark eyes the branched pigmented cells form a con- 
spicuous part. Within each lamella the bundles form plexuses. Near the termination, 



3 5 4 ATLAS OF HISTOLOGY. 

both of the radiating and meridional portion, but especially of the latter, the formation of 
plexuses becomes very marked, owing to the peculiar platelike enlargements of the 
muscle bundles; each of these gives off a number of thin, almost threadlike branches, 
which at the same time represent the terminations of the former (Ivanoff). Besides the 
network of capillaries, the ciliary muscle possesses a rich plexus of non-medullated nerve 
fibres, with which are connected numerous ganglion cells, either in small groups or in 
larger collections. 

The arterial branches of the ciliary processes and ciliary muscle are derived from 
the circulus arteriosus iridis major. In the ciliary processes the network of capillaries is 
very dense, and, corresponding to the elevations of these, forms conical groups, which, 
when viewed from the surface, are not unlike the capillary networks in the intestinal 
villi viewed obliquely. 

3. The Chorioidea. 

The chorioid membrane, being a continuation of the ciliary processes, contains a 
stroma of bundles of connective tissue, with numerous networks of elastic fibres and 
flattened branched pigmented cells. Counting from the sclerotic inwards, we meet with 
the following layers : — 

a) The lamina fusca ; this is a loose lamellar continuation of the scleral connective 
tissue, both fibrillar connective tissue and elastic networks. The connective-tissue cells 
are pigmented and unpigmented. The former are either large plates with few short and 
broad processes and oval nucleus, or they are small and possessed of numerous fine and 
branched processes, or they are altogether unbranched and more or less spheroidal. In 
the last instance the nucleus is spherical. The unpigmented cells are small flattened 
branched cells and endothelial plates, each with an oval nucleus, and covering the 
surface of the lamellae, as mentioned above. 

b) The lamina or membrana suprachorioidea is merely the continuation of the lamina 
fusca, but is considered part of the chorioidea both by right of custom and by the fact that 
when separating by force the sclerotic from the chorioidea it remains attached to the latter. 
Like the lamina fusca, it consists of lamellae of connective-tissue bundles, including networks 
of elastic fibrils. The lamellae, covered with endothelium, are separated from one another 
by large more or less continuous lymph-spaces. The fewer these lamellae the more con- 
siderable are the lymph-spaces (Schwalbe). The blood-vessels and nerves, running 
between the sclerotic and chorioidea, obtain on their passage a special sheath from the 
stroma of the lamellae. The connective-tissue cells of the lamellae of the lamina supra- 
chorioidea are of the same nature as those of the lamina fusca. 

c) Next to the lamina suprachorioidea follows a deep loose layer, containing the 



STRUCTURE OF THE CHORIOIDEA. 355 

larger blood-vessels, the stratum vasculosum of Loewe ; it is a continuation of a 
similar section of the ciliary processes. 

d) Then follows the elastic layer of Sattler. This observer finds in the human 
chorioidea, and also in that of many mammals, underneath or outwards of the chorio- 
capillaris, an endothelial membrane, then a stratum of elastic networks, generally without 
cells and containing the small branches of the arteries and veins. A second endothe- 
lial membrane separates it from the next following elastic layer, which generally 
contains branched pigment cells. 

c) Further comes the membrana chorio-capillaris, containing the dense network of 
capillaries. These vessels are ensheathed in a special layer of spindle-shaped and flattened 
cells, pigmented or unpigmented ; the former are either large flat plates with few broad 
short processes, or they are small with numerous fine long processes. The unpigmented 
cells are small and branched ; spheroidal cells, both with or without pigment granules, 
occur also here. 

f) A hyaline smooth lamina vitrea separates the chorio-capillaris from the uvea. 

g) This last, viz. the uvea, is considered a part of the retina. 

In the region of the ora serrata the uvea is covered with the pars ciliaris retinae, 
mentioned above. 

I vanoff mentions bundles of unstriped muscle cells which are to be met with even 
in the posterior parts of the chorioid membrane ; although outrunners of the meridional 
portion of the ciliary muscle, they are supposed by him to be independent muscular 
bundles belonging to the tissue of the chorioidea. 

According to Hallsten and Tigerstedt the chorioidea of man and many mammals 
(especially rabbit) possesses a continuous layer of unstriped muscle cells situated close to 
the outer surface of the chorio-capillaris, and probably identical with Sattler's inner endo- 
thelial membrane. The cells of this muscular membrane have a meridional direction, 
except at the entrance of the optic nerve and at the ora serrata, where they are arranged 

circularly. 

The dense network of capillaries of the membrana chorio-capillaris is derived from 
the arteriae ciliares breves and recurrentes. The vessels leading into the venae vorticosae 
are derived from the chorio-capillaris, from the iris, ciliary processes and the greater 

part of the ciliary muscle. 

The wall of the capillary blood-vessels of the chorio-capillaris is, like that of other 
capillaries, a single layer of elongated endothelial plates (Hallsten and Tigerstedt). 

The lymphatics will be considered in connection with those of the eyeball in 

general. 

3 f 



o: 



$6 



ATLAS OF HISTOLOGY 



CHAPTER XXXVII. 

THE LENS AND VITREOUS BODY. 

,. The lens of man and mammals is enclosed in a thick resistent elastic capsule, which 
in the fresh state and after reagents shows parallel to the surface very fine and dense striae. 
The capsule is thickest on the anterior surface, and diminishes in thickness towards the 
posterior pole. The posterior surface of the anterior capsule, that is the part covering 
the anterior surface of the lens substance, is lined with a single layer of hexagonal 
transparent granular-looking epithelial cells, each with a spherical or oval nucleus. 
When properly hardened the substance of the cells contains a delicate dense reticulum, 
and so does the nucleus, but it is less dense in the latter than in the former. 

The capsule covering the posterior surface is without any epithelial lining, and is in 
close contact with the substance of the lens. At the margin the nucleated hexagonal 
epithelial cells change into nucleated lens fibres, which gradually elongating run in a 
slightly curved direction from the posterior to the anterior surface. This condition is recog- 
nisable already in the earliest stages of the foetal lens. Passing then from the margin of 
the lens towards the posterior pole, we see in a bird's-eye view a similar hexagonal mosaic 
as on the anterior surface, but the latter is due to the hexagonal nucleated epithelial 
cells, while the former belongs to the ends of the lens fibres touching the posterior 
capsule. 

The substance of the lens is made up of the lens fibres and the interstitial substance. 
The lens fibres are bandlike structures passing from the posterior surface to the 
anterior, their posterior extremity is slightly enlarged and is in close contact with 
the posterior capsule, while the anterior one touches the epithelium of the anterior 
capsule. 

The fibres of the outer layers of the lens substance contain each an oval nucleus, 
visible under all conditions, those near the middle of the lens possess each a rudiment 
of a nucleus only demonstrable with strone acids. 

The nuclear zone of Mayer is the zone near the margin of the lens in which the 
lens fibres show a distinct nucleus, that is the region of transition of the epithelial cells 
into the lens fibres. 

In this zone the nuclei are situated in a curved plane belonging to the anterior half 
of the lens. 



STRUCTURE OF LENS FIBRES. 

0/ 

The lens fibres of the peripheral portions are broader and thicker than those in 
the centre, the former are softer and their substance less firm than that of the latter. 
Those In the centre or the so-called nucleus of the lens are firmest. In all parts they 
show a very delicate and dense longitudinal striatum. The shape of each lens fibre is 
that of a band, hexagonal in transverse section, but so that the two parallel surfaces 
are greatly larger than the other four. In a section that comprises a number of lens 
fibres transversely cut, a beautiful and regular hexagonal mosaic is obtained. 

The surface of the lens fibres is not smooth, but beset with minute ridges and 
furrows more or less regularly and closely distributed, the ridges of one lens fibre 
fitting into the furrows of its neighbour (Valentin, Henle, Kollikcr, Babuchin, Fubini, 
and others). These ridges and furrows are best marked on the narrower sides of the 
lens fibres— the short sides of the lens-hexagons— less so on the broad sides, although 
rudiments of them are also seen on the latter. Looking at the narrow sides of the lens 
fibres in the bird's-eye view a transverse striation is noticed. The fibres of the central 
part of the lens have larger and more irregular ridges and furrows than those ol the 
periphery. 

The lens fibres extend between the anterior and posterior surfaces of the lens 
and are arranged in concentric lamellae parallel to the surface. Each lamella consists 
of a single layer of lens fibres joined at their broad surfaces. Their extremities are 
slightly enlarged. At the two surfaces of the lens these extremities are in contact with 
one another in the sutures, or the rays of the so-called lens stars. In the lens of the new- 
born child the star both of the anterior and posterior surface consists of about three rays 
radiating alternately from the anterior and posterior pole towards the lens margin. 
In the lens of the adult each of the three rays possesses three or more secondary rays. 
These sutures extend from the surface of the lens towards the centre, and when viewed 
in the fresh organ appearas very fine and wavy lines, but after treatment witli hardening 
reagents, or better still after boiling, they appear as narrower or broader clefts. In the 
natural state these sutures contain a semifluid homogeneous interstitial cement-substance. 
The same substance is present between the lamellae, and also, though in a lesser quantity f 
between the fibres of the same lamella. This interstitial substance is the same as met 
with in all other organs.viz. the interfascicular substance of fibrous connective tissue, the 
cement-substance of epithelium and endothelium, of unstriped muscle cells, Sec. 

In the interlamellar cement-substance of the lens longer or shorter, broader or 
narrower channels may be met with in some places ; in transverse sections they appear as 
polyhedral discontinuities between the lamellae. Fine canals extend from them between 
the lens fibres of the same lamella. I therefore agree with O. Becker against Babuchin and 
Arnold that there exist channels in the interstitial substance, which probably have not 

3 F 2 



35 8 ATLAS OF HISTOLOGY. 

only an important bearing on the changes of the shape of the lens during accommoda- 
tion, but are also essential in the nutrition of the organ. 

2. The vitreous body is enclosed in a capsule, the membrana hyaloidea. This is a 
hyaline quite structureless delicate membrane. It increases in thickness towards the ora 
serrata, and forms here the Zonula ciliaris. It does not cover the fossa patellaris of 
the corpus vitreum (Ivanoff, Schwalbe), but passes from the margin of this latter to the 
margin of the lens as the Zonula Zinnii, thus forming the anterior wall of the lymphatic 
canal known as canalis Petiti. Like the rest of the hyaloidea, the Zonula ciliaris is 
hyaline, but contains longitudinal thin, and stiff elastic fibres, which over the ciliary 
processes and towards the root of the iris increase in number and thickness. They 
become at the same time grouped into bundles. In sections of hardened preparations 
the Zonula ciliaris remains adhering to the surface of the ciliary processes, and the 
bundles of its stiff fibres are very marked. 

Immediately underneath the hyaloidea are found isolated small granular-looking 
cells, each with a single or double transparent nucleus. These cells are the subhyaloid 
cells of Ciaccio. They are possessed of amoeboid movement (Ivanoff), and are met with 
not only in the region of the corpus vitreum, but also in that of the Zonula ciliaris. 
According to Ivanoff similar cells occur also between the hyaloidea and the retina. 

The substance of the corpus vitreum, that is the humor vitreus in man and mammals, 
appears, according to almost all observers (Brlicke, Hannover, Bowman, Doncan, Still- 
ing, Ivanoff, Gerlach, Smith, Schwalbe, and many others), arranged in layers separated 
from one another by clefts. These clefts possess in the peripheral parts a more con- 
centric arrangement, and they radiate from here towards the centre. According to 
more recent observers, especially Stilling, Ivanoff, and Schwalbe, these spaces are not 
lined with any membranous structures. 

In the centre of the adult corpus vitreum exists the canalis hyaloideus or canal of 
Stilling ; it extends from the papilla optici to the posterior capsule of the lens, and is 
lined with a hyaline membrane, a continuation of the membrana hyaloidea. It is not 
to be confounded with the canal of the embryonal corpus vitreum containing the arteria 
hyaloidea. 

Of solid structures there exist in the adult corpus vitreum few and scarce fibres ; 
they are the remnants of the embryonal vessels (Lieberkuhn). Ivanoff mentions in the 
region of the ora serrata fibres which are supposed by him to pass into the Zonula 
ciliaris of the hyaloidea, but this must be questioned. Schwalbe saw in the human 
corpus vitreum in one instance fine bundles of fibrils. 

Similar to the subhyaloid cells of the surface, mentioned above, there exist similar 
cells close to the membrane lining the canal of Stilling (Schwalbe). In the substance 



CELLS OF CORPUS VITREUM. 

^^;:~i::::;*:::r:- "—■ - - JZ 

,i , . J Possessed oi amoeboid movement, and include one 

two or three nuclei. They are accord i no- t n T «• • , 

v u j vu • , accordln g t0 ivanoff, either spherical, or more or less 

branched with or without nn P or h™ t , uuebS 

witnout one op two large vacuoles. Liebcrkttta and Schwalbe 
correctly «»■» tha, these cells are ail of , he sante kW , vi , colo „ rlc<s 1 
corpses the,, e*, s , a„ Intermediary forms b e,„ee„ them; ta wil „ va ™ 
probably degenerating forms. 



, 62 ATLAS OF HISTOLOGY. 

and after reagents (iodine-serum, osmic acid) the outer member exhibits fine longitudinal 
stria?, due to the presence of fine ridges and furrows (Hensen, M. Schultze), and also 
closely placed transverse stria?. After certain reagents, especially serum and dilute liquor 
potassfi, the outer member of each rod separates in a great many thin homogeneous- 
looking transverse discs (Hannover), owing to the swelling up of a cement-substance 
between the discs (M. Schultze). Ritter, Manz, Schiess, and others describe, after 
treatment with water and dilute chromic acid, a central filament in each outer member 
(Ritter's filament). The length of the outer member is generally greatest at the back 
of the eye, it diminishes towards the ora serrata. 

The outer extremity of the outer member is ensheathed, as mentioned above, by the 
filaments of the tapetum, it is as a rule rounded or slightly conical. 

The inner extremity is in contact with the inner member, from which it is separated 
by a thin layer of a cement-substance. When seen in profile the line of division is 
generally a straight one, but occasionally it is a broken one, and this is owing to the 
outer and inner member not joining in a single straight plane, their several extre- 
mities being facetted. But there is also another mode of junction between the two 
members, that is by a membranous sheath ; this is a continuation of the cortical sub- 
stance of the inner member and extending on and embracing the adjoining extremity of, 
the outer (Schwalbe). According to Landolt this sheath extends over the whole outer 
member of the batrachian rods. 

The inner member of the rods in man and mammals is cylindrical, but with convex 
surfaces ; it is broader than the outer one and about as long as the latter. 

In fishes and birds the inner member is more filamentous, but forming a bulbous enlargement 
at the point of junction with the outer member. In the frog's retina there are two distinct types of 
inner members, as I can fully confirm Schwalbe's observations ; one being filamentous and long 
and joined to a short outer member, the other short and thick and joined to a long outer member, 
Hoffmann observed the same relations also in the retina of Bufo and Bombinator, but not in 
Triton and Salamandra. 

The inner member is pale or indistinctly granular and shows a fine longitudinal 
striation due to the presence of fine fibrils which extend over it from the limitans 
externa in the shape of a basket-like sheath (Krause, M. Schultze). 

In the outer extremity of the inner member exists in many instances (birds, Krause ; 
many other vertebrates, M. Schultze) a peculiar lenticular structure, whose presence 
becomes very distinct after maceration in iodine-serum and osmic acid. 

In the human and mammalian retina, however, there exists in the cortical portion 
of the inner member, instead of the lenticular structure, a peculiar mass of longitudinal 
fine bright fibrils (M. Schultze). 



STRUCTURE OF THE CONES. 36 , 

According to Krause each inner member contains a central thread. 
Each cone consists like the rod of an outer short conical member and an inner 
longer and broader one, the body of the cone, with convex sides. The former con- 
tains within a delicate sheath (M. Schultze) a transparent substance which, just like that 
of the outer member of the rod, easily separates into a great many thin transverse 
discs. Also around the inner extremity of the body of the cones there projects from 
the limitans externa a basket-shaped arrangement of fibrils surrounding it like a sheath. 
The cortical substance of the body of the cones is also longitudinally striated (M. 
Schultze). 

I have been able to ascertain that in the frog's retina this striation of the cone- 
body and the inner member of the rods is in reality due to a fine reticulum arranged 
longitudinally. 

Where the inner member of the rods contains the above-named lenticular structure, 
the body of the cones possesses an elliptical one. Dobrowolsky saw this also in the 
cones of the human retina. 

After certain reagents, Mailer's fluid, iodine-serum, osmic acid, &c, the body 
of the cones of the ape (M. Schultze), of man (Krause, Hensen), and other mammals 
and birds (Krause), exhibits a central filament, which according to Krause is connected 
with the elliptical structure. 

The outer extremity of the body of the cones in most birds, reptiles, and amphibia, 
where it joins the outer member, contains a spherical corpuscle, which in most instances is 
coloured red, orange, yellow, green, or according to Krause and Dobrowolsky also blue. 
Hoffmann saw coloured globules in the inner members of the cones, also in the retina of 
Halmaturus. 

Double cones, each possessed of two outer and two inner members, the latter 
joined at their inner extremity, occur in the lower vertebrates, but not in mammals. 

The relation of the rods and cones as regards length varies in different animals; in 
man and most mammals the extremity of the outer member of the cones reaches as far as 
the middle of the outer member of the rods ; in the frog it does not pass much beyond 
the boundary between outer and inner member of the rods, while in fishes it extends 
nearly as far outwards as the outer member of the rods. 

The body of the cones is always thicker than that of the rods, and is nearly, if not 
quite, as long. 

The number of the rods is in man, most mammals, and also amphibia, and most 
fishes, greatly in excess of those of the cones, except in birds, where the opposite holds 
good. In the macula lutea of the retina of most vertebrates there exist only cones ; 
some fishes (shark and roach), and some mammals (bat, mole), do not possess any cones 

% G 



64 ATLAS OF HISTOLOGY. 

even in the macula lutea, while other vertebrates, as the owl, rat, mouse, guinea pig, 
and rabbit, possess only small and few cones. 

In the animals with cones in the macula lutea, the further away from this latter 

the fewer the cones. 

Both between the outer members of the rods and more distinctly between the latter 
and those of the cones there exists a homogeneous transparent albuminous substance 
which is fluid in the fresh and living state (Schwalbe, Henle, H. Miiller). 

Leydig observed first that the living retina possesses a red colour, but Boll investi- 
gated this more minutely in mammals and especially the frog, and found that in the 
living state and after preserving it in the dark, the retina possesses a purple red colour 
lodo-ed in the outer members of the rods. On the influence of the sunlight, this gradually 
makes room for a satiny lustre, and then altogether fades away. Retinas of eyes kept in 
the dark, or in red, or yellow light, easily separate from the pigmented epithelium, owing 
to an active retraction of the pigmented fibrils which in the ordinary state pass from the 
above cells between the rods, as described above. Kuhne and Ewald showed that 
this colour is originally purple, the visual purple, and is a pigment diffused in the 
outer members of the rods ; it can be isolated ; independent of the living state it can be 
reproduced when faded, by the contact with the pigmented epithelium ; the cones do not 
contain the visual purple, and in some retinae (Rhinolophus hyppoxideros, fowl, pigeon) 
also the rods are without it ; in the human retina and in that of the ape (Macacus cyno- 
glossus) the rods about the ora serrata are likewise without it ; where there exist 
numerous cones with coloured globules, the surrounding rods possess no visual purple. 
Boll found in the frog s retina, besides the purple rods, also a few of a bright green colour. 

In the human retina, in the living state and after death, provided the retina had 
in the latter instances been kept in the dark, the visual purple has been noticed by Boll, 
Kuhne, Schmidt-Rimpler, Adler, and Nettleship. Adler found that the presence of 
the visual purple is in direct proportion to the intact normal function of the retina. 

3. The Limitans Externa. 

The inner members of both rods and cones penetrate in a sharp line, which in 
profile view appears as a thin boundary line, through the limitans externa (M. Schultze), 
into the layer of the outer nuclei. The limitans externa possesses consequently smaller 
and larger holes, through which the members of both rods and cones respectively 
pass. Many of the rods and cones appear united with the limitans externa by minute 
lateral projections (Schwalbe). 

When viewed from the surface the limitans externa appears as a reticulated 
structure with fine striae in it (M. Schultze). From it issue fine fibrils to ensheath 



THE OUTER NUCLEAR LAYER. 365 

the inner extremities of the inner members of both rods and cones, as mentioned 
above. 

4. The Outer Nuclear Layer. 

Having passed the limitans externa, each rod and cone continues on its radial 
course through this layer as the rod- or cone-fibre respectively, and at the same time 
becomes a great deal thinner; this is especially the case with the rod-fibres, which 
resemble fine filaments. 

Each rod- and cone-fibre contains at one point an oval nucleus. Owing to the 
relative thinness of the rods and cones, and consequently owing to the relatively and 
absolutely great abundance of them, the number of layers of the nuclei forming the 
outer nuclear layer is very considerable ; in the retina of the batrachiae, owing to the 
thick rods and cones, the number of the nuclei is much smaller, being reduced to two, 
or at most three layers. 

In the retina of man and mammals the nuclei of the cone-fibres are in close contact 
with the limitans externa, while those of the rod-fibres are arranged in several layers 
further away. 

Owing to this relation, viz., the close position of the nucleus to the body of the 
cones in man and mammals, it follows that the outer portion of the cone-fibre, i.e. the 
part between the nucleus and the body of the cone, is very much shorter than the inner 
one, while in the rod-fibres the two portions, viz. the inner and outer, are both of an 
easily perceptible length. 

But this condition is not common to all vertebrates, for in batrachiae the relation is 
reversed, the nuclei of the rod-fibres lying in immediate contact with the limitans externa. 

About the macula lutea of the retina of man and mammals, where the number of 
rods becomes greatly reduced, of course also the layers of the nuclei diminish in 
numbers, especially in the inner parts of this, i.e. the outer nuclear layer; and there exists 
here a narrower or broader stratum between the above nuclei and the next following 
outer granular layer of the retina, in which only the inner portions of the cone-fibres 
are to be met with. This is Henle's outer fibrous layer. 

While the outer part of the rod-fibre is always the gradually attenuated continua- 
tion of the inner member of the rod, that of the cone-fibre often contrasts in a marked 
manner with the body of the cone, inasmuch as this latter appears to rest with a broad 
extremity on the limitans externa (Kolliker), while the cone fibre is here very thin. 
Thus it appears as if the cone-fibre were an independent thread penetrating into the 
body of the cone like its axial fibre (Krause and others). 

As regards the nuclei themselves, those of the rod-fibres differ from those of the 
cone-fibres*not only in position, as mentioned above, but also in their aspect. In man 

3 G2 



3 66 ATLAS OF HISTOLOGY. 

and mammals the nucleus belonging to a rod-fibre is, in the fresh state, and after many 
reagents, transversely striated (Henle, Krause, Ritter, and others), owing to its being 
apparently composed of some two or even three bands of a transparent hyaline 
substance alternating with two or three more highly refractive discs. Their limiting 
membrane is indistinct. The nucleus of a cone-fibre is on the other hand limited by a 
distinct membrane, is larger and has a clear contents, and in this may be recognised, 
after certain reagents (spirit, chromic acid), a pale transparent honeycombed reticulum. 

In the retina of the frog there is also a very marked distinction between the 

nuclei of the rod- and those of the cone-fibres ; the latter are more spherical, larger, do 

not possess any distinct limiting membrane, and include a uniformed fine reticulum, 

while the former are slightly smaller, oval, and within a definite limiting membrane 

contain a reticulum coarser and generally more or less shrunk away from the membrane, 

besides being always placed close to the limitans externa. 

Each rod- and cone-fibre at the boundary of the next inner layer of the retina, viz, 
the outer granular layer, possesses a conical enlargement (M. Schultze), which is very 
much more conspicuous in the cone-fibres than in those of the rods ; very fine fibrils 
come off from this enlargement, and penetrate into the granular layer, where they are 
lost. According to Max Schultze, these fibrils are nerve-fibrils. 

According to Merkel each cone-fibre passes directly into the outer process of the 
cells of the inner nuclear layer (see below). 

All these elements of the outer nuclear layer, viz. the rod-fibres and their nuclei, 
the cone-fibres and their nuclei, are embedded in a homogeneous honeycombed membra- 
nous matrix, which includes also a good many fibrils (Max Schultze) and whose spaces are 
of exactly the size and shape of the above nuclei. This honeycomb is in connection with 
the radial fibres of Muller (see below), and represents in fact the terminal membranous 
expansion of the latter. The limitans externa above mentioned is the outer boundary 
layer of this honeycombed matrix. 

The rods and cones with their respective fibres and nuclei represent the membrana 
Jacobi of the authors, they are in fact epithelial cells, peculiarly transformed (M. Schultze), 
and hence may be considered as the sensory epithelium (Schwalbe) analogous to the 
sensory epithelium in the olfactory, acoustic and taste organ, and, according to M-. 
Schultze, the above epithelial cells, are the real terminations of the nerves of the 
retina. 

All the layers of the retina internally to this sensory epithelium are developed, 
together with this latter, from the inner lamina of the optic cup. So that these layers, viz. 
the outer granular, the inner nuclear, and the inner granular layer, the ganglion-cells 
and the layer of nerve fibres, are comparable to a part of brain matter, modified in a 



THE OUTER MOLECULAR LAYER. , 6? 

certain manner, and pushed out towards the periphery (Hannover) ; hence Brtlcke's 
des.gnation of it as tunica nervea, or Henle s as stratum nerveum. 

5. The Outer Molecular Layer. 
The outer granular or molecular layer is a dense network of minute fibrils with 
vancosit.es (M. Schultze) ; they are embedded in a homogeneous ground substance. 
Both m vertical and horizontal sections the reticular nature of this layer is very distinct, 
and the granules between the fibrils are only the latter seen in optical section. In the 
outer portion of this layer, longer or shorter fibrils are met with which run for consider- 
able distances a horizontal course (M. Schultze, Hulke) and are possessed of minute 
varicosities. Embedded in, and intimately connected with the above reticulum are 
branched cells, flattened in a direction parallel to the surface (Golgi and Manfred.", 
Schwalbe, Krause), and containing a spherical clear nucleus. In the retina of the pike 
they are arranged in several layers of flattened endotheloid slightly branched cells 
(H. Miiller). 

The nature of the branched cells of this layer is considered by M. Schultze to be 

that of ganglion cells. 

The radial or Mailer's fibres (see below) penetrate vertically through this layer 
and appear on all sides connected with the reticulum by fine lateral branchlets 
(M. Schultze, Heinemann, Landolt), but according to Schwalbe, they (viz. Mullers 
fibres) pass simply through it (reticulum) without entering into any connection with it. 

6. The Inner Nuclear Layer. 

This layer differs in many respects from the outer nuclear layer, its nuclei being 
larger and in man and mammals arranged in fewer layers than those of the outer nuclear 
layer, while in the amphibia the reverse is the case, the inner nuclei forming more layers 
than those of the outer. 

The nuclei of the inner nuclear layer are of three different kinds : (a) very elon- 
gated transparent nuclei with a very distinct limiting membrane, they belong to the 
radial or Mullers fibres and lie either altogether within, or only closely at the side of 
them. (6) The greater number of nuclei of this layer are oval, placed with the long 
axis vertical to the surface ; in most instances they are without any distinct limiting 
membrane, and include a uniform honeycombed reticulum ; in the young retina (human 
as well as of mammals) many of them contain a nucleolus. These nuclei belong to 
spindle-shaped cells, the body of which is limited to a thin zone of protoplasm 
around the nucleus and drawn out at the poles into an outer and inner process. The 
outer is broad and branched and passes through the outer granular layer, while the 
inner is very thin, threadlike, and beset with minute varicosities ; it penetrates radially 



o 



6S ATLAS OF HISTOLOGY. 



into the next following inner granular layer, through which, according to Retzius and 

Schwalbe, it passes undivided. 

In the macula lutea the inner processes of these cells have not a radial direction, as 

in all other parts of the retina, but run a more oblique course (M. Schultze, H. Mtiller, 

Hulke and others). 

These cells are now considered by most observers to be bipolar ganglion cells 
(M. Schultze, Merkel, Schwalbe). According to Merkel they are of two different 
kinds : those connected with the cone-fibres and those connected with the rod- 
fibres. The former possess according to Merkel an unbranched, the latter a branched 
outer process. But in this latter statement he is contradicted by Kuhnt, according to 
whom all outer processes of the cells of the inner nuclear layer are branched. Kuhnt 
however confirms Merkel in the observation that they are connected either with the 
rod-fibres or with the cone-fibres. Also Gunn saw a connection of the cone-fibres with 
the outer processes of some of these cells. 

c) At the inner boundary of the inner nuclei is a layer of nucleated cells 
(Vintschgau) ; they are flattened and parallel to surface and are connected with one 
another in a network. These cells are particularly well shown, forming almost a 
separate layer, in the young retina both of man and mammals. 

The matrix of the inner nuclear layer is, just like that of the outer nuclear layer, 
a honeycomb of membranes and fibrils, intimately connected with the sides of the 
radial or Muller's fibres. The holes and channels of the matrix are occupied by the 
above bipolar ganglion cells. 

7. The Inner Granular or Molecular Layer. 

This layer is always much thicker than the outer granular layer, with which it coin- 
cides in structure, viz. being a dense reticulum of very fine fibrils (M. Schultze, Kolliker, 
Manz and others). In birds and amphibia this layer appears stratified, owing to the 
reticulum being much denser in some horizontal planes than in those between 
(M. Schultze). 

Into this reticulum pass from inwards the processes of the ganglion cells and 
through it penetrate in a radial direction Muller's fibres; according to some (Max 
Schultze) they give off to it lateral branchlets, while others (Retzius, Schwalbe, Hoff- 
mann, Emery) deny such a connection (see below). The processes of the gan- 
glion cells may be traced into the inner parts of the granular layer for a longer or 
shorter distance in a radial, oblique, or even horizontal manner, branching on this way 
and ultimately altogether losing themselves in the reticulum. As mentioned above, 
the varicose inner processes of the bipolar ganglion cells of the inner nuclear layer 



THE LAYER OF GANGLION CELLS. 369 

pass through the inner granular layer in a radial direction. Retzius and also Schwalbe 
consider these the only nerve fibrils passing through this layer. 

According to M. Schultze and others the reticulum of both the outer and inner 
granular layer is partly supporting (connective-tissue), partly nervous tissue ; but according 
to Schwalbe the whole reticulum is supporting tissue. Golgi and Manfredi found in 
this layer the same branched, flattened cells as in the outer granular layer. 

8. The Layer of Ganglion Cells. 

Except in and around the macula lutea the ganglion cells are arranged in a single 
layer. In the former they form several layers. In man and mammals the ganglion 
cells are conspicuous by their large size ; in that of the batrachiae they are very small, 
the cell substance being reduced to a thin layer around the nucleus. This latter is in 
all instances large and spherical, and limited by a distinct membrane. Its contents are a 
clear substance with a more or less distinct honeycombed reticulum, and in the young 
state one or two nucleoli (Schwalbe). Also these nucleoli include a delicate dense 
reticulum (Frommann). The cell-substance is like that of other ganglion cells, a network 
of fibrils (M. Schultze). Their processes are of two kinds : (a) each ganglion cell sends 
generally one process towards the next following layer of nerve-fibres (Bowman) and 
becomes in fact continuous with a nerve fibre (Corti, Kolliker, H. Muller and others) ; occa- 
sionally this process is double and both pass into nerve fibres ; (6) towards the inner granu- 
lar layer each ganglion cell sends off one or two branched processes : these break up 
entirely into fine fibrils, identifying themselves with the reticulum of the inner granular 
layer (M. Schultze). But according to Retzius, Manz, Schwalbe, and others, this process 
or processes pass simply through the inner granular layer and reach the inner nuclear 
layer. The ganglion cells anastomose with one another in some instances (Corti, Steinlin, 
Santi Sirena). 

The ganglion cells are separated from one another by the radial or Mailer's 
fibres, which, while passing here give off lateral fibrous membranous homogeneous 
structures, anastomosing into a sort of honeycomb, in whose meshes lie the ganglion cells ; 
their processes are surrounded by a clear fluid albuminous substance. A few flattened 
nucleated cells (Golgi and Manfredi) besides the blood-vessels, to be mentioned below, 
are also contained in this layer. 

9. The Layer of Nerve-Fibres. 
This layer is thickest immediately around the papilla nervi optici in a direction 
vertically upwards and downwards, and still more so at the sides (Liebrich) ; it gradu- 
ally diminishes in thickness towards the ora serrata. In the macula lutea the nerve fibres 



ATLAS OF HISTOLOGY. 

•J I 

do not exist as a complete layer, being greatly interrupted by the many layers of ganglion 

cells. 

At the entrance into the plane of the retina the bundles of the nerve fibres of the 

optic nerve curve round from a horizontal into a vertical direction and pass on as the 
nerve-fibre layer, the bundles radiating from the papilla nervi optici towards the whole 
circumference of the retina. They always remain grouped in bundles (Kolliker), which 
in many places are arranged as a plexus (Michel). 

The nerve fibres at the point of entrance into the retina, or rather, already in the 
level of the lamina cribrosa of the eyeball, lose, as a rule, their medullary sheath and 
throughout the retina pursue their course as simple axis-cylinders of very different thick- 
nesses ; after certain reagents they exhibit more or less regular varicosities (M. 

Schultze). 

In the rabbits retina there are two bundles of nerve fibres with medullary sheath 

passing from the optic nerve into the retina (Bowman). 

In the human retina and that of the mammals it is exceptional to find medullated 
nerve fibres, even in the neighbourhood of the papilla nervi optici. 

The connective tissue band which includes the central blood-vessels of the optic 
nerve, may be followed for a short distance into the nerve-fibre layer of the retina as 
thin bundles of connective tissue between the nerve-fibre bundles. Further away the 
nerve bundles are separated from one another by the same lymph-spaces that have 
been mentioned in Chapter XIV. p. 100, of the optic nerve, containing also the flat 
nucleated cells, described there as neuroglia cells. According to Schwalbe, they are 
more of the character of endothelial cells. 

Numerous fine fibrils arranged in horizontal networks have been observed in this 
layer by Kuhnt ; they anastomose by means of fine trabecular with the reticulum of the 
inner granular layer, with which they are indentical in their nature. 

10. The Membrana Limitans Interna. 

The inner boundary of the retina is formed by the inner extremities of the radial or 
Miiller's fibres, just as the limitans externa of M. Schultze is the outer boundary layer 
of the honeycombed matrix into which the outer extremities of the radial fibres of 
M tiller break up. 

The fibres of Mtiller are pyramidal structures, which with their broad bases are in 
close contact and thus form a complete inner boundary of the retina, the limitans interna 
(Schwalbe). These bases are of various sizes, and when viewed from the surface in 
suitable preparations, e.g. in those stained with nitrate of silver, appear as a mosaic of 



THE FIBRES OF MULLER. 2?l 

more or less polygonal fields of various sizes, and thus resemble an endothelium 
(W. Norris and Shakespeare), without however bein^ one 

Each fibre of Muller possesses at its inner extremity, and while passing through 
the nervous layer, a pyramidal enlargement, which becomes attenuated in the layer of 
the ganglion cells. As mentioned previously, it passes through all the other layers in a 
radiating manner and terminates at the limitans externa. 

In the inner nuclear layer each Miiller's fibre is possessed of a nucleus, as described 
above, and this forms the boundary between what is regarded as the inner and outer 
portion, the former belonging to the layer of nerve fibres, ganglion cells, and the inner 
granular layer, while the latter extends through the rest of the retina to the limitans 
externa. According to the digestion-experiments of Kuhnt, the two portions are 
chemically different from one another. The nucleus belonging to the Miiller's fibre in 
the inner nuclear layer appears in some instances as if applied to the surface only of the 
fibre, that is, as if it belonged to a cell fixed on the fibre. This condition may be 
observed, not only on the radial fibres of the frogs retina (Manz, Schwalbe), but 
also in that of mammals and man. 

In the layer of the nerve fibres and ganglion cells, but especially in the former, each 
pyramidal enlargement gives off laterally membranous, homogeneous structures, as well 
as fibrils ; by these they anastomose with one another and with the honeycombed matrix 
of those layers. The substance of the radial fibres is longitudinally striated and 
each contains in the pyramidal extremity an oval clear nucleus. 

The connection of the radial fibres of Muller with the matrix of the reticulum 
in the inner and outer granular layer, and with the honeycombed stroma of the inner 
and outer nuclear layer has been mentioned above. 

it. The Macula Lutea and Fovea Centralis. 

This part of the retina of man and apes owes its yellow colour to the presence of a 
diffuse yellow pigment present only between the elements of the retina (M. Schultze). 

The difference between the layers of the macula lutea and of the surrounding 
portions of the retina have been mentioned already above, viz. the absence of rods 
and of a continuous nerve-fibre layer, the presence of several layers of ganglion cells, 
and the great length and curved or oblique direction (Bergmann) of the cone-fibres 
in the macula lutea. 

As has been mentioned above, there being no rods here, the nuclei are wanting in 
the inner part of the outer nuclear layer, and this is entirely occupied by the inner 
portions of the cone-fibres, thus forming Henle s outer fibrous layer. 

The cones of the macula lutea are thinner than in the surrounding parts, and, when 

3 « 



s92 ATLAS OF HISTOLOGY. 

viewed from the surface, stand in beautiful curved lines, converging towards the centre 
of the macula lutea (M. Schultze). 

In the fovea centralis of all layers the cones and outer nuclei only retain their 
position. The cones become much attenuated and extremely long. The cone-fibres are 
also very long and pass in an almost horizontal direction into the inner nuclear layer 
at the side of the fovea centralis. 

The inner nuclear layer, and that of the ganglion cells, is altogether wanting, and 
only a thin continuation of the inner granular layer is continued over the fovea centralis. 

12. The Ora Serrata. 

The layers of the retina terminate rather abruptly, and only the radial fibres of 
Muller, or their inner pyramidal extremities, becoming shortened and broader and 
more smooth on their surface, are continued as columnar transparent epithelial-like 
cells (Schwalbe), each with an oval nucleus. This forms the pars ciliaris retinae, which, 
as stated on a previous page, can be traced over the processus ciliares up to the root of 
the iris. 

The substance of the cells is more or less distinctly longitudinally striated ; the 
nucleus, in many instances, contains within a definite membrane a spongy honeycombed 
reticulum and one large central nucleolus. 

13. The Blood-vessels. 

The capillaries of the retina are connected with the branches of the arteria and 

vena centralis nervi optici. 

In the optic nerve the central blood-vessels are surrounded by a special plexus of fine nerve 
fibres (Krause). 

The larger vascular branches surround the macula lutea and send into it minute 
twigs. At the margin of the fovea centralis the capillaries return as loops. 

The arterial and venous branches are situated internally to, or within the nerve- 
fibre layer. The capillaries are arranged in networks with large meshes. They occur 
in the inner granular layer: one network near the inner nuclear layer, the other near 
the layer of ganglion cells ; then there is a capillary network in the inner nuclear layer, 
and the most superficial capillaries are found in the outer granular layer. 

14. The Lymphatics. 

His was the first to show that the blood-vessels of the retina (chiefiy the veins and 
capillaries) are invaginated in lymph-spaces, perivascular lymph-spaces. According to 



THE LAMINA CRIBROSA. m 

Schwalbe they can be injected from the lymphatics of the optic nerve, that is, by 
injecting underneath the pial sheath of this latter. 

The lymph-channels between the bundles of the nerve-fibre layer have been 
mentioned above ; they maybe also injected from the lymphatics of the optic nerve 
(Schwalbe), and for obvious reasons radiate from the papilla nervi optici. 

15. The Lamina Crtbrosa, 

Where the optic nerve joins the retina, the sclerotic and chorioidea enter a very 
intimate relation with its sheath as lamina cribrosa. That sheath and its lymph-spaces, 
as well as the structure of the optic nerve, have been fully described in Chapter XIV. 
pp. 99 and 100. 

It seems misleading to speak of a ' perforation of the membranes of the eyeball (sclerotic 
and chorioidea) by the optic nerve,' as the optic nerve has been connected with the retina already 
since the primary optic vesicle of the embryo, and the sclera and chorioidea, which develop at a 
later period, close, as it were, around the point of junction of the optic nerve and the retina. 

In the frog the sclera and chorioidea, although closing round the optic nerve, do not penetrate 
into it as a lamina cribrosa, but in the mammalia and man early in the embryo the tissue of 
the sclera and chorioidea, especially of the former, penetrates into the optic nerve at the point of 
its junction with the retina. 

The outer or dural sheath (Key and Retzius) of the optic nerve passes into the 
outer strata of the sclerotic, its connective-tissue trabecule being directly continuous 
with one another (Donders) ; while the middle or arachnoidal sheath and the inner or 
pial sheath pass into the inner strata of the sclerotic, only few trabecule of the pial 
sheath anastomose with those of the chorioidea. 

In the level of the sclerotic many thinner and thicker trabecule of connective 
tissue, derived from the inner strata, pass in a transverse direction between the bundles 
of the optic nerve. Here they anastomose with the longitudinal connective-tissue septa 
between the bundles of nerve fibres, which, as mentioned on p. 100, are continuous 
with one another and the pial sheath. These transverse bundles form a network, and 
thus constitute the chief part of the lamina cribrosa; in pigmented eyes, especially in 
the dark eyes of mammals, they carry with them large numbers of branched pigment 
cells, also arranged transversely. 

The longitudinal septa between the bundles of the optic nerve at the entrance into the 
lamina cribosa, and while in this latter, contain very numerous nucleated cells, especially abundant 
in the young retina (Wolfring). 

The lamina cribrosa receives undoubtedly a few thin trabecule with pigmented cells 
from the chorioidea, although many histologists (Donders, Klebs, Henle, Schwalbe) 
deny this participation. 



374 ATLAS OF HISTOLOGY. 

Outside the dural sheath of the optic nerve exists the supravaginal lymph-space. 
The subdural space of the optic nerve communicates with the supravaginal space by 
the lymph-canalicular system of the dural sheath (Michel). 

The supravaginal space passes into the Tenonian lymph-space (Schwalbe), 
mentioned above as existing between the inner lamella of the Tenonian capsule fixed 
on the outer surface of the sclerotic and the outer lamella composed of the connective 
tissue surrounding the eyeball. 

The subdural lymph-space of the optic nerve (subvaginal space of Schwalbe) 
extends a short distance into the sclerotic between its outer and inner section it is 
generally slightly larger than the subdural space and terminates with an attenuated 
margin (Jager, Michel). The sub-arachnoidal space of the sheath of the optic nerve 
anastomoses at the level of the lamina cribrosa with the lymph-spaces between the pial 
sheath and the nerve bundles (see p. roo), by means of lymph-clefts (lymph-canalicular 
system) of the pial sheath (Schwalbe) ; the intrabulbar end of the subarachnoidal 
space of the optic nerve communicates with the perichorioidal lymph-space of Schwalbe 
which, as has been mentioned on a former page, extends between the sclerotic and 
chono.dea and is permeated by a spongy mass of trabecular, covered with endothelium 
and contammg numerous networks of elastic fibrils. This communication between the 
two spaces is established by means of interfascicular lymph-clefts (lymph-canalicular 
system) passmgin an oblique direction through the inner strata of the sclerotic (Michel) 
The penchorioidal lymph-space or lymph-spaces communicate with the Tenonian 
space by means of l ymp hatics invaginating the venous vessels passing from the 
chono.dea outwards (venae verticosae). The interfascicular lymph-spaces of the sclerotic 
communicate both with the perichorioidal and Tenonian lymph-space (Waldeyer) 

The anterior chamber of the eye does not seem to communicate directly, either 
*J£Z 0riOida ' 0rthC Te " 0nlan '—- or with the lymphatic vessels of 

sclero^c e a C n dT UniCat ;° n " "^ "* * "*" ° f ^ ^ *~» ° f ^ —a, 

_sc erofc, and hgamentum pectmatum. Injections into the anterior chamber pass also 

mto the anterior ciliary veins (Schwalbe, Heisrath). 

According to the observations of Knies and W P ,« ti 
t i . ^ines ana Weiss, there exists a current nawlno- 

fro™ h tenorchamb „ of theeye tiM , n 2 "J "« 

.no, t „e,,™ of Ae merob™ Descend to, the I ymph . cana , icula 

cornea, «■*»**. spaces of ,„, .^^ ^^ ^ ^ J£~ 

J; "£■? th ; post r ior parts ° f the ■»*» *« e, ta . curren « from behind 

lurwara including - the subsfanr^ nf +u~ j 

V- Of its posterior llaI f ^ ^'^ '° W ^ "* *« —- ' 



the 
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STRUCTURE OF THE SKIN. 375 

PLATE XLI. 

Fig. I. From a vertical section through the skin at the volar side of the human 
finger. Magnifying power about 40. 

1. Stratum corneum. 

2. Stratum lucidum. 

3. Stratum granulosum. 

4. Stratum Malpighii. 

5. Papillary layer of the corium. 

6. An interpapillary process of the stratum Malpighii continued as the duct of a 
sweat gland and cut away obliquely. 

7. The subcutaneous tissue containing the coiled tube of the sweat glands. 

8. The adipose tissue. 

9. A Pacinian corpuscle in transverse section. 

10. Sweat-gland tubes cut in various directions. 

11. An arterial trunk cut transversely. 

12. The mouth of a sweat-gland duct. 

13. A tactile or Meissner's corpuscle. 

Fig. II. Part of a dog's sweat gland. Magnifying power about 350. 

1. The wall of the gland tube is seen from above ; it shows a layer of longitudinal 
very thin unstriped muscle cells. 

2. The duct is lined with a cuticle and a layer of nucleated polyhedral cells. The 
point where it opens into the gland tube is well marked by the alteration in size and by 
the difference of the lining epithelium. 

Fig. III. A part of the layer 7 of figure I. highly magnified (about 400), to show 
the structure of the coiled tube of the sweat gland. This consists of two different portions, 
a proximal and distal one. The former is nearer the duct, possesses the same structure 
as this, but differs from it by being coiled ; its lumen is lined with a thick homo- 
geneous membrane ; then follow several layers of small polyhedral cells, of which only 
the nuclei are here shown. A limiting membrana propria forms the outer boundary. 
The distal portion is composed of a coiled tube much broader than the former ; its lining 
epithelium is a layer of columnar transparent or longitudinally striated cells. Between 
this and the limiting membrana propria is a longitudinal layer of thin unstriped muscle 
cells. 



37 6 ATLAS OF HISTOLOGY. 

i. Proximal part of the coiled tube in longitudinal, 

2. The same in transverse section. 

3. Distal part cut longitudinally. 

4. The same cut transversely. The muscular cells inside the membrana propria 
are not represented with sufficient distinctness. 

5. Fat-cells. 

Fig. IV. Coiled tube of sweat gland in section, from the ear-lobe of pig. Magni- 
fying power about 300. 

1. A hair-follicle in transverse section. 

This is cut at the papilla, which with its capillary blood-vessels is seen in the 
centre ; it is surrounded by the cells — indicated by its nuclei — of the bulb of the hair. 
Then follows a thick layer of nuclei indicative of the cells of the external root-sheath, 
and finally the inner coat of the hair-sac. Between the bulb of the hair and the external 
root-sheath is seen at one side a rudiment of the inner root-sheath in the form of a layer 
of flattened cells. 

2 and 3. The coiled tube in transverse and oblique section. The layer of un- 
striped muscle cells between the lining epithelium and the membrana propria is well 
shown. 

Between the coils of the tube is fibrous connective tissue with many capillary 
blood-vessels. 

Fig. V. From a vertical section through the scalp of a fully developed human 
embryo, showing a papillary hair and its root-sheaths. The figure comprises the 
region of the neck, but not that of the mouth of the hair-follicle. Magnifying power 
about 300. 

1. The substance of the hair. 

2. The inner root-sheath. Between 1 and 2 the cuticle of the hair. 

3. The layers of the outer root-sheath. 

4. The rudiment of the sebaceous gland. 

5. The papilla, its cells indicated by their nuclei. 

6. The bulb of the hair ; the outlines of its polyhedral cells are marked by brown 
pigment granules embedded in the interstitial cement-substance. As the cells of the 
bulb elongate to form the cells of the hair substance, also the configuration of the inter- 
cellular pigmented cement-substance alters accordingly. 

7. The transverse layer of unstriped muscle cells of the hair-sac, indicated here by 
their nuclei. 



STRUCTURE OF THE HAIR-FOLLICLE. 377 

8. The layers of polyhedral cells from which the cuticle of the hair and the various 
layers of the inner root-sheath are developed and at whose expense they continue to 
grow. 

9. A layer of spindle-shaped cells, here cut transversely because they are arranged 
transversely on the long axis of the hair. 

10. Cells continuous with the cuticle of the hair and the cuticle of the inner root- 
sheath. 

1 1. Cuticle of the hair. 

12. Thick homogeneous-looking inner root-sheath; its division into Henle's and 
Huxley's layer is not shown here. 



Fig. VI. Longitudinal section through a bed-hair of the lip of a newborn child. 

Magnifying power about 90. 

1. Stratum corneum of the epidermis. 

2. Stratum Malpighii. 

3. Hair shaft projecting from the mouth of the hair-follicle. 

4. The outer root-sheath. 

5. The rudiment of the sebaceous gland. 

6. The enlargement of the outer root-sheath around the hair-knob. 

7. The rudiment of the new hair, being an outgrowth of the outer root-sheath ; it is 
surrounded by the unstriped muscle cells of the hair-sac. 

8. The rudiment of the new papilla. 



Fig. VII. Longitudinal section through a bed-hair of the adult human scalp, 
Magnifying power about 60. 

1. Epidermis of the mouth of hair-follicle. 

2. Hair shaft. 

3. Outer root-sheath. 

4. Alveoli of the sebaceous gland. 

5. Musculus arrector pili. 

6. A cystic outgrowth of the outer root-sheath. 

7. The hair-knob. 

8. The rudiment of the new hair. 

9. The rudiment of the new papilla. 



378 ATLAS OF HISTOLOGY. 

Fig. VIII. Surface view of part of the outer root-sheath of a cilium of a newborn 
child, to show the branched cells between the epithelial cells of the outer root-sheath. 
Magnifying power about 300. 

Fig. IX. Longitudinal section through a papillary hair of the adult human scalp. 
Magnifying power about 60. 

1. Epidermis of the general surface ; only its stratum Malpighii is here indicated. 

2. The mouth of the hair-follicle. 

3. The alveoli of the sebaceous gland. 

4. The bundles of the arrector pili. 

5. The papilla. 

6. Adipose tissue, 

PLATE XLII. 

Fig. X. Transverse section through two hairs of the paw of a fcetal kitten. 
Magnifying power about 300. 

A is a section through a thicker hair and is further away from the hair-papilla 
than B. 

1. The cells of the substance of the hair. 

2. The cuticle of the hair. 

3. The cuticle of the inner root-sheath. 

4. The inner or Huxley's layer, 

5. The outer or Henle's layer. 

6. The cells of the outer root-sheath, indicated by their nuclei. 

7. The circular layer of the hair-sac. 

8. Lymph-space, 

9. The surrounding connective tissue. 

Fig. XI. Longitudinal section through the hair of the lip of a fcetal rabbit. 
Magnifying power about 300. 

1. The hair-papilla is indicated by the nuclei of its cells ; a few branched cells are 
seen amongst them, similar ones are also extending between the cells of the hair 
bulb. 

2. The hair-bulb, its cells indicated by their nuclei. 

3. The marginal layer of cells of the outer root-sheath at the bulb. 



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STRUCTURE OF THE HAIR. 379 

4 and 5. The cells from which the inner root sheath is formed. 

6. The layer of transversely arranged spindle-shaped cells, which have been 
referred to in the text as resembling unstriped muscle cells. 

7. The outer root-sheath. 

8. The rudiment of the inner root-sheath. 

9. The hair substance. 

Fig. XII. From a longitudinal section through a cilium 'of a newborn child. 
Magnifying power about 400. 

1. The hair substance, rows of pigment granules in it ; the marrow is indicated as 
a clear central part with a few (large) groups of air-bubbles. 

2. The cuticle of the hair. 

3. The inner root-sheath, its constituent parts not differentiated here. 

4. The cell-layers constituting the outer root-sheath. 

5. The glassy membrane. 

6. Intraepithelial connective-tissue cells. 

Fig. XIII. A sebaceous gland from a vertical section through the lip of mouth of 
the sheep. Magnifying power about 200. 

1. The duct. 

2. The branches of it. 

3. The alveoli. 

The minute details of structure of the cells of the alveoli are not indicated here 
The distinction between the nucleated cells filling the alveoli themselves and their 
remnants in the branches of the duct is here too sharp. 

Fig. XIV. From a section through a lobule of fcetal subcutaneous fat-tissue. 
Magnifying power about 450. 

1. Part of the connective-tissue septum between two fat-lobules. 

2. Lymph-space. 

3. A capillary blood-vessel. 

4. Fat-cells in various stages of formation, filled with oil globules, dissolved out in 
the preparation from which this drawing is obtained. Some of the cells are distinctly 
possessed of processes. 



Fig. XV. Transverse section through the hair of ear lobe of the pig. Magnifyin 
power about 350. 

31 



38o ATLAS OF HISTOLOGY. 

i. The pigmented substance of the hair. 

2. The cuticle of the hair. 

3. Huxley's layer of the inner root-sheath. 

4. Henle's layer of it. Many of the cells of both contain a remnant of a nucleus. 

5. The cell-layers of the outer root-sheath. 

6. The marginal layer of columnar cells with oval nuclei. 

Fig. XVI. Transverse section through the hair and hair-follicle of the adult 
human scalp. Magnifying power about 350. 

1. The marrow. 

2. The pigmented substance of the hair. 

3. The cuticle of the hair ; next to this is a delicate line, indicating the cuticle of 
the inner root-sheath. 

4. Huxley's layer. 

5. Henle's layer of the inner root-sheath. 

6. The outer root-sheath. 

7. The glassy membrane ; next to this is the circular coat of the hair-sac. 

8. A lymph-space between the circular coat of the hair-sac and the connective 
tissue forming its outer coat. 

Fig. XVII. Vertical section through the eyelid of a newborn child. Magni- 
fying power about 25. 

1. The conjunctiva palpebral ; its epithelium is indicated as a purple line. The 
mucosa is represented much too thick. 

2. The mouth of the duct of a Meibomian gland. 

3. The cilia. 

4. The skin of the lid ; sweat glands and hairs are only faintly indicated as prolon- 
gations of the stratum Malpighii. 

5. The bundles of the sphincter orbicularis in transverse section. 

6. The inner and outer bundles of the musculus ciliaris Riolani ; between the two 
passes the duct of the Meibomian gland. The alveoli of this latter appear all cut away 
in various directions. 

Fig. XVIII. From a vertical section through the ligamentum pectinatum iridis 

and the adjoining portion of the sclerotic and ciliary muscle. Magnifying power 
about 200. 

1. The spongy mass of elastic trabecular forming the matrix of the ligamentum 







VIII 



■■'*■' 






LIGAMENTUM PECTIN A TUM. 381 

pectinatum. The nuclei seen on them correspond to the endothelial cells covering 
them. 

2. The meridional portion of the ciliary muscle. 

3. The spaces in the spongy matrix of the ligamentum pectinatum. 

4. The canal of Schlemm, lined with an endothelial membrane and ei vine ofl to 
the right a narrow channel. 

5. The bundles of the sclerotic in transverse section ; between them are seen the 
nuclei of the connective-tissue corpuscles and networks of elastic fibrils joining those of 
the trabecular of the ligamentum pectinatum and o{ the tendon of the ciliary muscle. 

Fig. XIX. From a vertical section through the anterior layer of the cornea of a 
newborn child. Magnifying power about 350. 

1. The stratified pavement epithelium. 

2. The deepest layer of columnar cells. 

3. The anterior elastic membrane of Bowman. 

4. The anterior strata of the substantia propria, with the corneal corpuscles seen in 
profile. 

Fig. XX. From a vertical section through the anterior layers of the cornea of 
the rabbit after staining with chloride of gold. Magnifying power about 200. 

r. The stratified epithelium ; many of the intraepithelial nerve fibrils are shown, 
especially those which run horizontally, that is parallel to the surface, in the superficial 
layer. 

2. Long fine nerve fibrils of the subepithelial network derived from a thick 
branch further down. Some of them appear as if belonging to the deepest layer of 
the epithelium, but this is due to the fact that fibrils are here shown which in reality lie 
underneath the epithelium. 

3. The anterior strata of the substantia propria. 

PLATE XLIII. • 

Fig. I. From a vertical section through the anterior portion of the cornea of the 
rabbit, stained with chloride of gold and hematoxylin. Magnifying power about 400. 

1. The stratified anterior epithelium. 

2. Bowman's membrane. 

3. Substantia propria ; the connective-tissue ground-substance is indicated as of a 



ATLAS OF HISTOLOGY. 

uniform tint in it a few elastic fibrils ; the corneal corpuscles are seen in profile, and there- 
fore appear as thin elongated corpuscles. A nerve branch ascends obliquely from the depth 
and near Bowman's membrane gives off fine fibrils. In this latter are seen three black 
dots ; they are transverse sections through fine nerve fibrils running in that membrane 
in a horizontal direction. A thin ramus perforans passes right through Bowman's 
membrane on the left of the figure, and gives off fine fibrils running closely underneath 
the epithelium and forming part of the subepithelial network. A few intraepithelial 
nerve fibrils ascend between the columnar cells of the deepest layer. 

Fi^. 1 1. From a vertical section through the same cornea, but showing the posterior 
layers. 

i. The endothelium of Descemet's membrane. 

2. Descemet's membrane. 

3. The substantia propria ; the corneal corpuscles in their lymph canalicular system 
are well shown. Some of the canaliculi join the lacunae of different strata. 

Fig. III. From a vertical section through the anterior part of the cornea of the 
dog. Magnifying power about 300. 

1. The stratified epithelium. 

2. A delicate Bowman's membrane. 

3. The substantia propria. Between longitudinally cut bundles of the connective- 
tissue matrix there are shown numerous others cut transversely. The lacunae with the 
corneal corpuscles are shown in profile. 

Fig. IV. From a horizontal section through the cornea of the rabbit, stained with 
chloride of gold, showing the superficial layer of the epithelial cells, indicated by their 
oval nuclei only, and underneath it the fine intraepithelial nerve fibrils. Magnifying 
power about 400. 

Fig. V. A few pigmented epithelial cells of the uvea of a processus ciliaris of 
a newborn child, seen from the surface. The clear interstitial cement-substance is well 
marked. Magnifying power about 300. 

Fig. VI. From a horizontal section through the substantia propria of the frog's 
cornea, stained with chloride of gold. Magnifying power about 450. 

1. Fine nerve fibrils terminating in a minute network, not in, but on a corneal 
corpuscle. 



MEMBRANES OF THE EVE, 383 

2. A second corneal corpuscle simply crossed by nerve fibrils. On the right the 
nerve fibril does not actually terminate in the substance of the corpuscle ; it is in 
reality above the corpuscle. 

Fig. VII. From a meridional section through the eye of the ox. Magnifying 
power about 30. 

1. Cornea, 

2. Conjunctiva, at the limbus containing diffuse adenoid tissue. 

3. Sclerotic ; the connective-tissue corpuscles contain much pigment. 

4. Root of iris. 

5. Ciliary muscle ; only its meridional portion is here shown. 

6. Ciliary process. 

Fig. VIII. From a meridional section through the eye of a child. Magnifying 
power about 40. 

1. Cornea. 

2. Sclerotic. 

3. Iris. 

4. Ciliary process. 

5. Ligamentum pectinatum. 

6. Meridional portion of the ciliary muscle, its bundles forming plexuses. The 
radiating portion is shown as minute dots— because transversely cut— between the 
meridional portion and the ciliary process. 

7. Chorioidea. 

8. Retina of the ora serrata. 

9. Sphincter pupilke. 

Fig. IX. From a meridional section through the eye of a sheep. Magnifying 
power about 30. 

1. Cornea, 

2. Conjunctiva of the limbus. 

3. Sclerotic. 

4. Iris ; the pigment of its tissue and of its anterior epithelium has been omitted. 

5. Ciliary process. Numerous folds are seen on the posterior surface of this as 
well as of the iris. 



384 ATLAS OF HISTOLOGY. 

6. Chorioidea with the uvea. 

7. Retina. 

Fig. X. From a vertical section through the ciliary processes of the eye of the ox. 
Magnifying power about 200. 

1. Dense fibrous matrix with pigmented connective-tissue corpuscles 

2. Loose connective tissue ; the capillary blood-vessels in it are omitted. 

3. The uvea. 

4. Pars ciliaris retinae, a layer of columnar cells. 

5. Zonula ciliaris with bundles of fibres in it. 

Fig. XI. From a meridional section through the eye of an albino rabbit. Mag- 
nifying power about 60. 

1. Cornea. 

2. Conjunctiva of the limbus. 

3. Sclerotic. 

4. Ligamentum pectinatum. 

5. Root of the iris. 

6. Ciliarv processes, covered with the unpigmented uvea ; its cells appear stratified 
because viewed obliquely. 

7. Meridional portion of the ciliary muscle. 

Fig. XII. A few of the cells of the pars ciliaris retinae of the same preparation 
as in Figure X., but viewed from the top. The markings between the cells are not per- 
fect ; the nucleus of the cells contains a distinct reticulum and nucleolus. Magnifying 
power about 660. 

PLATE XLIV. 

Fig. XIII. From a horizontal section through the rabbit's cornea, stained with 
chloride of gold, showing two oval nuclei of the superficial epithelial cells, and fine 
nerve fibrils terminating in a very delicate network. Magnifying power about 660. 

Fig. XIV. From a horizontal section through the substantia propria of a rabbit's 
cornea, stained with chloride of gold, showing several corneal corpuscles and fine nerve 
fibrils crossing them. Magnifying power about 450. 

Fig. XV. Branched pigmented connective-tissue corpuscles of the tissue of the 
iris of the ox, seen from the surface. 

Fig. XVI. The same seen in profile. 











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LENS AND CHORIOIDEA. 385 

Fig. XVII. Pigmented connective-tissue cells of the deep tissue of the chorioidea 
of the same eye ; the cells are very little branched. Magnifying power in all three 
figures about 350. 

Fig. XVIII. From a transverse section through the lens of a dogs eye, showing 
the lens fibres transversely cut and arranged in strata. The three angular openings cor- 
respond probably to lymph channels running parallel with the lens fibres. Magnifying 

power about 350. 

Fig. XIX. Copy of part of Figure IX. by hvanoff in the ' Handbuch d. gesam. 
Augenheilkunde,' by Graefe and Saemisch, part i. p. 280. Showing groups of ganglion- 
cells in the nerve plexus of the chorioidea of an adult. 

Fig. XX. Transverse section through the chorioidea of the ox. Magnifying 
power about 250. 

1. Chorio-capillaris. Outside this is a layer of elastic fibrils, Sattler's layer, 
shown on the left side of the figure. 

2. The layer of large veins, venae vorticosre. 

3. The outer layer containing numerous pigmented connective-tissue cells flattened 
in a direction parallel to the surface. 

Fig. XXT. From a vertical section through the eye of a sheep's foetus. Magni- 
fying power about 30. 

1. The rudiment of the eyelid. 

2. The sclerotic continued into the cornea. 

3. The outer layer of the optic cup, or the pigmented epithelium of the retina. 

4. The rudiment of the retina. 

5. The epithelium lining the anterior capsule of the lens. At the margin the cells 
pass into the lens fibres. The nuclear zone of the latter is well shown. 

6. The posterior portion of the lens fibres. 

7. The rudiment of the corpus vitreum with capillary blood-vessels. 

Fig. XXII. From a transverse section through the eye of the sheep. Magnify- 
ing pow r er about 100. 

1. Inner portion of the sclerotic. 

2. Suprachorioidal lymph-space, permeated by lamella with pigmented cells. 

3. Outer layer of the chorioidea, containing numerous pigment cells. 

4. Sattler's layer. 



ATLAS OF HISTOLOGY. 

386 

5. The tapetum nigrum, or epithelium of the retina. 

6. The layer of the rods and cones. 

7. Limitans externa. 

8. The outer nuclear layer. 

9. The outer granular or outer molecular layer. 

10. The inner nuclear layer. 

11. The inner granular layer. 

12. The layer of the ganglion cells. 
1 a The layer of the nerve fibres. 

The radial or MUlle* fibres passing through the two last-named layers are well 

shown. 

Fig . XXIII. Transverse section through the retina of the dog. Magmfymg 

power about 350. 

1. The rods and cones. 

2. Limitans externa. 

3. The outer nuclei. 

4. The outer granular layer. 

5. The inner nuclei. 

6. The inner granular layer. 

7. The ganglion cells. 

8. The nerve fibres. _-„„ t 

9 . The limitans interna, being composed of the ends of the radial or Mullers 

fibres. 

Fi. XXIV. Copy of part of fig. XVI. from Schwalbe in ' Handbuch d. ges. 
Augenh.' by Graefe and Sameisch, p. 37 . , showing part of the inner surface of the human 
retina, stained with argentum nitricum. On the right side the radial fibre-cones project 
with their free basis. 

Fie XXV. From a vertical section through part of the frog's retina. Magnifying 
power about 350. 

1. The outer member of the rods. 

2. The inner member, between them the cones. 

3. The limitans externa. 

4. The honeycombed matrix, in whose meshes are contained the outer nuclei. 

5. A nucleus belonging to a connective-tissue corpuscle at the inner boundary of 
the reticular outer granular layer. 



LAYERS OF THE RET/A A. ^ 

6. A few of the inner nuclei. The spindle-shaped cells of which they form part 
have been omitted. 

Fig. XXVI. Two radial Mailer's fibres of the retina of the rabbit. Magnifying 
power about 400. 

1. The layer of the outer nuclei. 

2. The layer of the inner nuclei. The oval nuclei here shown belong to the radial 
fibres. 

3. The connection of the radial fibres with the matrix of the inner granular 
layer. 

4. The region of the ganglion cells. Here the radial fibres overlap each other in 
the preparation, and appear therefore in the drawing as if they formed a single fibre. 
The inner extremity of the fibres is not shown. 

Fig. XXVII. From a vertical section through the retina of the rabbit. Magnify- 
ing power about 400. 

1. The region of the outer nuclei. 

2. The outer granular layer. 

3. The inner nuclei. 

4. The nucleus of a connective-tissue corpuscle. 

5. The inner granular layer. Its reticular matrix is well shown. 

6. The inner extremities of the radial or Muller's fibres. 

7. The limitans interna formed by the inner free surface of the radial fibres. 

Fig. XXVIII. A ganglion cell from the same retina as that represented in fig. 
XXIII. Magnifying power about 660. 

1. The outer processes of the ganglion cell terminate apparently in the reticulum 
of the inner granular layer. 

2. The body of the ganglion cell. 

3. Nerve fibres. 

Fig. XXIX. Two ganglion cells of the same retina as in the preceding figure. 

1. Inner granular layer. 

2. The ganglion cells. 

3. A blood-vessel in transverse section. 

3 K 



388 ATLAS OF HISTOLOGY. 

4. A portion of a Mailer's fibre indicated only. 

5. The nucleus of a connective- tissue corpuscle. 

Fig. XXX. Transverse section through the frogs retina. Magnifying power 
about 150. 

1. The pigmented epithelium of the retina; the outer part is unpigmented and 

includes the oval nucleus. 

2. The outer members of the rods, ensheathed in the pigmented filaments of the 
cells of the epithelium. 

3. The inner members of the rods and the cones between them. 

4. The region of the limitans externa. 

5. The outer nuclei. 

6. The outer granular layer. 

7. The inner nuclei. They are represented incorrectly too small. 

8. The inner granular layer, showing stratification. 

9. The nuclei of the ganglion cells. 

10. The nerve fibres. 

The pyramidal extremities of the radial fibres are well shown. 



;39 



CHAPTER XXXIX. 

THE OUTER AND MIDDLE EAR. 

The cartilaginous matrix of the auricula has been described in Chapter VI 1 1, as reticular 
or elastic cartilage. The skin covering it is in no way different from that of other parts. 

It is continued into the meatus auditorium externus, where it differs in so far as the 
ordinary sweat glands are replaced by the larger ceruminous glands, which have been 
described in a former chapter, p. 315. 

Towards the membrana tympani the hairs and their sebaceous glands become 
scarcer, and the corium much thinner. The subcutaneous tissue in both the cartila</i- 
nous and osseous portion is so firmly connected with the connective tissue of the peri- 
chondrium or periosteum respectively, that it may be regarded as part of these. 

The cartilage of the meatus auditorius externus is elastic cartilage, bein£ a direct 
continuation of the cartilage of the auricula. 

The Membrana Tympani. 

The membrana tympani consists of an outer, middle, and inner lamella. The first 
is a direct continuation of the skin of the meatus auditorius externus, the second is the 
membrana propria, and the third is the mucosa. The skin part is a delicate membrane 
composed of delicate bundles of connective tissue covered with a thin epidermis. This 
last-named differs in no way in structure from that of the meatus auditorius externus. 
The papillae of the corium present in this latter do not pass beyond the margin, i.e. the 
tendinous ring of the membrana tympani, except at the posterior upper part, where 
they extend as far as the processus brevis of the malleus. 

The membrana propria, or middle stratum, contains, besides a limited number of 
elastic fibrils and elastic membranes (Helmholz), stiff bundles of connective tissue 
similar to tendinous tissue grouped as larger or smaller trabecular. They possess cither 
a radiating arrangement, as in the layer next to the cutis, or a circular one, as in that 
next to the mucosa, or they pass in various directions and branch out either into the 
one or the other. 

Some of those of the outer and inner layer run out into the skin part and into the 
mucosa. 



390 ATLAS OF HISTOLOGY. 

Between the trabecule are left longer or shorter clefts, and larger or smaller sac- 
cular sinuses lined with endothelium, and forming an inter-communicating system of 

lymphatic vessels (Kessel). 

The membrana propria is wanting in the fissure or notch of Rivini. 

The mucosa is a very delicate connective-tissue membrane, covered with a single 
layer of squamous nucleated epithelial cells ; groups of small cells are interspersed 
amongst the others. Small stomata exist between them (Kessel). 

The blood-vessels form capillary networks for the skin part as well as for the 
mucosa, and for the membrana propria ; these networks anastomose with each other 
(Gerlach, Kessel, and others). The venous vessels empty themselves into the plexus of 
veins at the margin of the membrana tympani, and into the venous plexus surrounding 
the handle of the malleus. 

The lymphatics are also arranged in three layers (Kessel) ; 

a) A subepithelial network of fine vessels in the cutis. 

b) A similar one in the mucosa ; and 

c) The inter-communicating system of wide lymphatics of the membrana propria. 
The latter anastomose with either of the other two. 

There is a lymph-canalicular system of lacunae and canaliculi in the connective 
tissue of the mucosa and membrana propria of the same nature as that described of the 
serous membranes (Kessel). 

Kessel found also that the movement of the membrana tympani assists in the 
absorption by the lymphatics from the tympanic cavity. 

The (non-medullated) nerves are arranged as plexuses of the cutis, of the membrana 
propria, and of the mucosa. The finest fibres form a subepithelial network both for 
the cutis and the mucosa, and from it pass fibrils amongst the epithelial cells (Kessel). 

The capillary blood-vessels are everywhere